├── .github └── workflows │ └── ci.yml ├── README.md ├── docs ├── cgroups.md ├── devices.md ├── favicon.png ├── files.md ├── index.md ├── namespaces.md ├── network.md ├── processes.md ├── security.md ├── shell.md ├── signals.md ├── syscalls.md └── system.md ├── mkdocs.yml └── overrides └── main.html /.github/workflows/ci.yml: -------------------------------------------------------------------------------- 1 | name: ci 2 | on: 3 | push: 4 | branches: 5 | - main 6 | jobs: 7 | deploy: 8 | runs-on: ubuntu-latest 9 | steps: 10 | - uses: actions/checkout@v2 11 | - uses: actions/setup-python@v2 12 | with: 13 | python-version: 3.x 14 | - run: pip install mkdocs-material 15 | - run: mkdocs gh-deploy --force 16 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | Questions to test your Linux knowledge. 2 | 3 | ## Table of Contents: 4 | 5 | 1. [cgroups](https://katademy.github.io/linux-faq/cgrou[s]) 6 | 1. [devices](https://katademy.github.io/linux-faq/devices) 7 | 1. [files](https://katademy.github.io/linux-faq/files) 8 | 1. [namespaces](https://katademy.github.io/linux-faq/namespaces) 9 | 1. [network](https://katademy.github.io/linux-faq/network) 10 | 1. [processes](https://katademy.github.io/linux-faq/processes) 11 | 1. [security](https://katademy.github.io/linux-faq/security) 12 | 1. [shell](https://katademy.github.io/linux-faq/shell) 13 | 1. [signals](https://katademy.github.io/linux-faq/signals) 14 | 1. [syscalls](https://katademy.github.io/linux-faq/syscalls) 15 | 1. [system](https://katademy.github.io/linux-faq/system) 16 | 17 | #### Like this project? 18 | 19 | * [Leave a Star](https://github.com/katademy/linux-faq/stargazers) 20 | * Follow [@katademy](https://twitter.com/katademy) on Twitter 21 | * Donate via [PayPal](https://paypal.me/icelynjennings) or [Patreon](https://patreon.com/icelynjennings) 22 | -------------------------------------------------------------------------------- /docs/cgroups.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | _____ of memory cgroups trigger an Out-of-Memory killer inside them. A process will get killed when it goes above them. 4 |

5 | Hard limits 6 |

7 | 8 |

9 |

10 | Can cgroups limit I/O devices/operations usable by a process? _____ 11 |

12 | Yes 13 |

14 | 15 |

16 |

17 | Can cgroups limit network bandwidth usable by a process? _____ 18 |

19 | Yes 20 |

21 | 22 |

23 |

24 | The file /proc/[pid]/cgroup contains the process's _____ 25 |

26 | enclosing control group 27 |

28 | 29 |

30 |

31 | _____ allow you to set resource limits on processes and their children. 32 |

33 | cgroups 34 |

35 | 36 |

37 |

38 | _____ cgroup limits are not enforced. 39 |

40 | soft 41 |

42 | 43 |

44 |

45 | The _____ (crowd control) cgroup allows to freeze/thaw a group of processes, much like it is done by SIGSTOP signals. Unlike signals however, it CANNOT be detected by the processes. This is useful for cluster batch scheduling and process migration. Doesn't impede ptrace/debugging. 46 |

47 | freezer 48 |

49 | 50 |

51 |

52 | Can cgroups limit memory usable by a process? _____ 53 |

54 | Yes 55 |

56 | 57 |

58 |

59 | Each cgroup can have its own _____ or hard limits 60 |

61 | soft 62 |

63 | 64 |

65 |

66 | The _____ cgroup controls what a group can do what on device nodes (read/write/mknod permissions etc). You can do it on /dev/net/tun, /dev/fuse, /dev/kvm, /dev/dri so you can have network interface manipulation, filesystems in user space, VMs and GPUs inside containers. Example: allow /dev/xxxx deny everything else 67 |

68 | device 69 |

70 | 71 |

72 |

73 | "The _____ cgroup keeps track of pages used by each group. Each page is """"charged"""" to a group and can be shared across groups. file (read/write/mmap from block devices) anonymous (stack, heap, anonymous mmap) active (recently accessed) inactive (candidate for eviction)""" 74 |

75 | memory 76 |

77 | 78 |

79 |

80 | _____ allow limiting the amount of resources usable by a process. 81 |

82 | cgroups 83 |

84 | 85 |

86 |

87 | When processes inside a Linux system are running out of memory, lower priority processes might be randomly killed by the kernel to free memory up. A _____ cgroup ensures that whenever a process inside it is running out of memory, only the processes inside that cgroup will be up for deletion in such a situation - never the ones outside it. 88 |

89 | memory 90 |

91 | 92 |

93 |

94 | Can a CPU cgroup set CPU weights? _____ 95 |

96 | Yes 97 |

98 | 99 |

100 |

101 | _____ cgroups pin groups of processes to a specific cpu or reserve cpus to specific apps, preventing processes from switching around CPUs. 102 |

103 | cpuset 104 |

105 | 106 |

107 |

108 | A _____ cgroup keeps track of user system cpu time, and usage per cpu. 109 |

110 | CPU 111 |

112 | 113 |

114 |

115 | The file _____ contains the process's enclosing control group 116 |

117 | /proc/[pid]/cgroup 118 |

119 | 120 |

121 |

122 | Do cgroups limit the resources a process can use (in quantity)? _____ 123 |

124 | Yes 125 |

126 | 127 |

128 |

129 | The _____ cgroup keeps track of IO for each group. You can set throttle limits and relative weights for each group. 130 |

131 | blkio 132 |

133 | 134 |

135 |

136 | _____ cgroups automatically set traffic class or priority for traffic generated by processes in the group. (only works for egress traffic) net_cls will assign traffic to a class (which then has to be matched with iptables) 137 |

138 | net_cls and net_prio 139 |

140 | 141 |

142 |

143 | "When a process needs to perform a root-account specific action, but you don't want it to have root account permissions, _____ can be set in order to """"break down"""" the root account into multiple fine-grained permissions.""" 144 |

145 | capabilities Nevertheless, the CAP_SYS_ADMIN capability cannot be disabled 146 |

147 | 148 |

149 |

150 | Linux Containers are usually a combination of _____ 151 |

152 | cgroups, namespaces, SELinux, AppArmor 153 |

154 | 155 |

156 |

157 | The command _____ can be used to move a process to a cgroup 158 |

159 | echo $PID > /sys/fs/cgroup/.../tasks 160 |

161 | 162 |

163 |

164 | The command echo $PID > /sys/fs/cgroup/.../tasks _____ 165 |

166 | can be used to move a process to a cgroup 167 |

168 | 169 |

170 |

171 | Each cgroup can have its own soft or _____ limits 172 |

173 | hard 174 |

175 | 176 |

177 |

178 | Can you make a cgroup limit any kind of memory? (e.g. physical, kernel, total memory...) _____ 179 |

180 | Yes 181 |

182 | 183 |

184 |

185 | Can cgroups limit CPU time usable by a process? _____ 186 |

187 | Yes 188 |

189 | 190 |

191 |

192 | Each cgroup can have its own soft or hard _____ 193 |

194 | limits 195 |

196 | 197 |

198 |

199 | Can a CPU cgroup set CPU limits? _____ 200 |

201 | No 202 |

203 | 204 |

205 |

206 | PID 1 is placed at the root of each cgroup. Are its children created inside the parent's groups? _____ 207 |

208 | Yes 209 |

210 | 211 | -------------------------------------------------------------------------------- /docs/devices.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | The command free _____ 4 |

5 | displays memory usage 6 |

7 | 8 |

9 |

10 | The command _____ displays memory usage 11 |

12 | free 13 |

14 | 15 |

16 |

17 | The directory /media predominantly contains _____ 18 |

19 | mounted external devices such as USB drives 20 |

21 | 22 |

23 |

24 | The mount type _____ is one-directional. 25 |

26 | slave 27 |

28 | 29 |

30 |

31 | The /dev directory predominantly stores _____ 32 |

33 | device files 34 |

35 | 36 |

37 |

38 | The mount type _____ is private and cannot be replicated. 39 |

40 | unbindable 41 |

42 | 43 |

44 |

45 | The command vmstat _____ 46 |

47 | reports virtual memory statistics 48 |

49 | 50 |

51 |

52 | The mount type _____ is not shown unless mounted. 53 |

54 | private 55 |

56 | 57 |

58 |

59 | The command umount _____ 60 |

61 | unmounts a specified device 62 |

63 | 64 |

65 |

66 | The command _____ unmounts a specified device 67 |

68 | umount 69 |

70 | 71 |

72 |

73 | The command _____ reports virtual memory statistics 74 |

75 | vmstat 76 |

77 | 78 | -------------------------------------------------------------------------------- /docs/favicon.png: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/katademy/linux/57f9f7aad2f4dd9d69d593cb820344255521e8a5/docs/favicon.png -------------------------------------------------------------------------------- /docs/files.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | The command _____ displays disk usage and limits 4 |

5 | quota 6 |

7 | 8 |

9 |

10 | The command _____ lists text files that only have 1 character in their name 11 |

12 | ls ?.txt 13 |

14 | 15 |

16 |

17 | The command touch used on an existing file will _____ 18 |

19 | change its timestamp to the latest date and time 20 |

21 | 22 |

23 |

24 | "The command _____ lists all files whose names begin with the letter """"a"""", and their second letter is either """"b"""" or """"c" 25 |

26 | ls a[bc] 27 |

28 | 29 |

30 |

31 | The command _____ updates a file's timestamp if it exists, and does nothing if it doesn't exist 32 |

33 | touch -c 34 |

35 | 36 |

37 |

38 | The command touch -c _____ 39 |

40 | updates a file's timestamp if it exists, and does nothing if it doesn't exist 41 |

42 | 43 |

44 |

45 | The command _____ changes file attributes 46 |

47 | chattr 48 |

49 | 50 |

51 |

52 | The command cut -c2 _____ 53 |

54 | would print the second column in a text file 55 |

56 | 57 |

58 |

59 | The command file _____ 60 |

61 | can determine a file's type 62 |

63 | 64 |

65 |

66 | The command _____ finds directories within the current directory 67 |

68 | find . -type d 69 |

70 | 71 |

72 |

73 | You can't make hard links across filesystem boundaries because their _____ might be identical. 74 |

75 | inodes 76 |

77 | 78 |

79 |

80 | An alias file for an existing file with identical inode is called a _____ 81 |

82 | hard link 83 |

84 | 85 |

86 |

87 | A file _____ indicates an I/O resource such as a file, pipe or network socket. 88 |

89 | descriptor 90 |

91 | 92 |

93 |

94 | The command _____ lists the contents of a directory 95 |

96 | ls 97 |

98 | 99 |

100 |

101 | The command _____ can mount a file system 102 |

103 | mount 104 |

105 | 106 |

107 |

108 | The command _____ can search files for lines that match a pattern 109 |

110 | grep 111 |

112 | 113 |

114 |

115 | The command _____ searches files for lines that match a pattern 116 |

117 | fgrep 118 |

119 | 120 |

121 |

122 | The command mount _____ 123 |

124 | can mount a file system 125 |

126 | 127 |

128 |

129 | The command _____ continously prints newly added lines of a file 130 |

131 | tail -F 132 |

133 | 134 |

135 |

136 | The command cat _____ 137 |

138 | displays a file's contents 139 |

140 | 141 |

142 |

143 | The command _____ searches for a program in the directories listed in the user's PATH environment variable 144 |

145 | which 146 |

147 | 148 |

149 |

150 | The command ls -R _____ 151 |

152 | lists a folder's subdirectories 153 |

154 | 155 |

156 |

157 | The directory /bin contains _____ 158 |

159 | boot binaries in single user mode 160 |

161 | 162 |

163 |

164 | The command fdisk _____ 165 |

166 | manipulates partition tables 167 |

168 | 169 |

170 |

171 | The _____ file lists filesystems and partitions mounted at boot time. 172 |

173 | /etc/fstab 174 |

175 | 176 |

177 |

178 | The command rcp _____ 179 |

180 | copies files between two machines. 181 |

182 | 183 |

184 |

185 | When RAM runs out, _____ is used. 186 |

187 | swap space 188 |

189 | 190 |

191 |

192 | The command _____ original.txt copy.txt copies a file 193 |

194 | cp 195 |

196 | 197 |

198 |

199 | The command _____ searches for a program 200 |

201 | whereis 202 |

203 | 204 |

205 |

206 | The command rm _____ 207 |

208 | removes files 209 |

210 | 211 |

212 |

213 | The command fgrep _____ 214 |

215 | searches files for lines that match a pattern 216 |

217 | 218 |

219 |

220 | The command find . -type f _____ 221 |

222 | finds files within the current directory 223 |

224 | 225 |

226 |

227 | The command fsck _____ 228 |

229 | checks and repairs filesystem consistency 230 |

231 | 232 |

233 |

234 | /usr/bin stores _____ 235 |

236 | executable programs 237 |

238 | 239 |

240 |

241 | The command ls -al _____ 242 |

243 | displays the long list of files inside folder, including hidden files 244 |

245 | 246 |

247 |

248 | The command _____ displays the differences between two files 249 |

250 | diff 251 |

252 | 253 |

254 |

255 | The command _____ displays a file's contents 256 |

257 | cat 258 |

259 | 260 |

261 |

262 | The command tar -xf _____ 263 |

264 | extracts a tar file 265 |

266 | 267 |

268 |

269 | The command _____ sets the default permission of new files 270 |

271 | umask 272 |

273 | 274 |

275 |

276 | The command _____ runs the commands from a file 277 |

278 | source 279 |

280 | 281 |

282 |

283 | The command _____ changes the current working directory 284 |

285 | cd 286 |

287 | 288 |

289 |

290 | The command _____ manipulates partition tables 291 |

292 | fdisk 293 |

294 | 295 |

296 |

297 | The command du _____ 298 |

299 | estimates space usage for each file 300 |

301 | 302 |

303 |

304 | The command diff _____ 305 |

306 | displays the differences between two files 307 |

308 | 309 |

310 |

311 | The command _____ scans a file system for disk usage 312 |

313 | quotactl 314 |

315 | 316 |

317 |

318 | The command source _____ 319 |

320 | runs the commands from a file 321 |

322 | 323 |

324 |

325 | The command pwd _____ 326 |

327 | prints the present working directory 328 |

329 | 330 |

331 |

332 | The three first file descriptors are: _____ 1 stdout 2 stderr 333 |

334 | 0 stdin 335 |

336 | 337 |

338 |

339 | The command which _____ in the directories listed in the user's PATH environment variable 340 |

341 | searches for a program 342 |

343 | 344 |

345 |

346 | The command split _____ 347 |

348 | splits a file into pieces of specified size 349 |

350 | 351 |

352 |

353 | The command _____ creates a symbolic link to a file 354 |

355 | ln 356 |

357 | 358 |

359 |

360 | Does each file have its own inode? _____ 361 |

362 | Yes 363 |

364 | 365 |

366 |

367 | The command _____ can divide a file into several parts 368 |

369 | cut 370 |

371 | 372 |

373 |

374 | The command _____ sets disk quotas 375 |

376 | quotacheck 377 |

378 | 379 |

380 |

381 | The command _____ estimates space usage for each file 382 |

383 | du 384 |

385 | 386 |

387 |

388 | The command _____ displays free disk space 389 |

390 | df 391 |

392 | 393 |

394 |

395 | The command _____ displays the long list of files inside folder, including hidden files 396 |

397 | ls -al 398 |

399 | 400 |

401 |

402 | "The command _____ lists all text files whose names start with an """"A" 403 |

404 | ls [A]*.txt 405 |

406 | 407 |

408 |

409 | The command _____ can search for files that meet specified criteria 410 |

411 | find 412 |

413 | 414 |

415 |

416 | The command _____ merges two files interactively 417 |

418 | sdiff 419 |

420 | 421 |

422 |

423 | The directory _____ contains boot binaries in single user mode 424 |

425 | /bin 426 |

427 | 428 |

429 |

430 | Does a file's inode store its access, change and deletion timestamps? _____ 431 |

432 | Yes 433 |

434 | 435 |

436 |

437 | The command tee _____ 438 |

439 | can redirect output towards multiple files 440 |

441 | 442 |

443 |

444 | The command which searches for a program in _____ 445 |

446 | the directories listed in the user's PATH environment variable 447 |

448 | 449 |

450 |

451 | The command ls _____ 452 |

453 | lists the contents of a directory 454 |

455 | 456 |

457 |

458 | The command find . -type d _____ 459 |

460 | finds directories within the current directory 461 |

462 | 463 |

464 |

465 | The command sort < unsorted.txt _____ 466 |

467 | pipes an unsorted.txt file into the sort command 468 |

469 | 470 |

471 |

472 | "The command ls [A]*.txt _____" 473 |

474 | lists all text files whose names start with an """"A 475 |

476 | 477 |

478 |

479 | The command ln _____ 480 |

481 | creates a symbolic link to a file 482 |

483 | 484 |

485 |

486 | Does a file's inode store the file's creation timestamp? _____ 487 |

488 | No 489 |

490 | 491 |

492 |

493 | The command head -1 file.txt _____ 494 |

495 | outputs the first line of a file 496 |

497 | 498 |

499 |

500 | Does a file's inode store its file type? _____ 501 |

502 | Yes 503 |

504 | 505 |

506 |

507 | The command _____ finds files within the current directory 508 |

509 | find . -type f 510 |

511 | 512 |

513 |

514 | The command _____ can create a hard link 515 |

516 | ln 517 |

518 | 519 |

520 |

521 | The command sort _____ 522 |

523 | sorts contents of a file 524 |

525 | 526 |

527 |

528 | The directories /lib and /lib64 predominantly store _____ 529 |

530 | Program code libraries 531 |

532 | 533 |

534 |

535 | /sbin and /usr/sbin directories contain _____ 536 |

537 | system administration binaries (FDisk, FSCH, ifconfig, init, makefs, shutdown, halt) 538 |

539 | 540 |

541 |

542 | The command umask _____ 543 |

544 | sets the default permission of new files 545 |

546 | 547 |

548 |

549 | The three first file descriptors are: 0 stdin 1 stdout _____ 550 |

551 | 2 stderr 552 |

553 | 554 |

555 |

556 | The command tar -cf _____ 557 |

558 | creates a tar file 559 |

560 | 561 |

562 |

563 | An _____ is a data structure that stores relevant information about a file. 564 |

565 | inode 566 |

567 | 568 |

569 |

570 | The command _____ outputs the last line of a file 571 |

572 | tail -1 file.txt 573 |

574 | 575 |

576 |

577 | The three first file descriptors are: 0 stdin _____ 2 stderr 578 |

579 | 1 stdout 580 |

581 | 582 |

583 |

584 | The command ls ?.txt _____ 585 |

586 | lists text files that only have 1 character in their name 587 |

588 | 589 |

590 |

591 | The command _____ sorts contents of a file 592 |

593 | sort 594 |

595 | 596 |

597 |

598 | The command _____ makes a secure, remote file copy. 599 |

600 | scp 601 |

602 | 603 |

604 |

605 | The command _____ used on an existing file will change its timestamp to the latest date and time 606 |

607 | touch 608 |

609 | 610 |

611 |

612 | The command chattr _____ 613 |

614 | changes file attributes 615 |

616 | 617 |

618 |

619 | "The command find . -name ""abc*"" _____" 620 |

621 | finds files that have the partial string ""abc"" in the name 622 |

623 | 624 |

625 |

626 | The command quotacheck _____ 627 |

628 | sets disk quotas 629 |

630 | 631 |

632 |

633 | The command _____ helps recover data, especially after using dd 634 |

635 | ddrescue 636 |

637 | 638 |

639 |

640 | The command _____ can convert a full pathname to just a path 641 |

642 | dirname 643 |

644 | 645 |

646 |

647 | The command _____ can display when a file was last accessed 648 |

649 | stat 650 |

651 | 652 |

653 |

654 | Does a file's inode store its size? _____ 655 |

656 | Yes 657 |

658 | 659 |

660 |

661 | The command mv _____ 662 |

663 | can move or rename files and directories 664 |

665 | 666 |

667 |

668 | Does a file's inode store its ACLs? _____ 669 |

670 | Yes 671 |

672 | 673 |

674 |

675 | "The command ls a[bc] _____" 676 |

677 | lists all files whose names begin with the letter """"a"""", and their second letter is either """"b"""" or """"c 678 |

679 | 680 |

681 |

682 | The command _____ would print the second column in a text file 683 |

684 | cut -c2 685 |

686 | 687 |

688 |

689 | The command quota _____ 690 |

691 | displays disk usage and limits 692 |

693 | 694 |

695 |

696 | The directory /etc predominantly stores _____ 697 |

698 | configuration files 699 |

700 | 701 |

702 |

703 | The directory /tmp predominantly stores _____ 704 |

705 | Temporary files created by the system 706 |

707 | 708 |

709 |

710 | The command df _____ 711 |

712 | displays free disk space 713 |

714 | 715 |

716 |

717 | The command _____ creates a tar file 718 |

719 | tar -cf 720 |

721 | 722 |

723 |

724 | The command wc _____ 725 |

726 | gets a file's word count 727 |

728 | 729 |

730 |

731 | The command mkdir _____ 732 |

733 | creates new folders 734 |

735 | 736 |

737 |

738 | The command _____ copies files between two machines. 739 |

740 | rcp 741 |

742 | 743 |

744 |

745 | The command _____ splits a file into pieces of specified size 746 |

747 | split 748 |

749 | 750 |

751 |

752 | _____ directories contain system administration binaries (FDisk, FSCH, ifconfig, init, makefs, shutdown, halt) 753 |

754 | /sbin and /usr/sbin 755 |

756 | 757 |

758 |

759 | The target path of a symlink is stored in the file's _____ 760 |

761 | inode 762 |

763 | 764 |

765 |

766 | The command _____ lists a folder's subdirectories 767 |

768 | ls -R 769 |

770 | 771 |

772 |

773 | The command _____ removes files 774 |

775 | rm 776 |

777 | 778 |

779 |

780 | _____ stores executable programs 781 |

782 | /usr/bin 783 |

784 | 785 |

786 |

787 | "The command _____ finds files that have the partial string ""abc"" in the name" 788 |

789 | find . -name ""abc*"" 790 |

791 | 792 |

793 |

794 | The command find _____ 795 |

796 | can search for files that meet specified criteria 797 |

798 | 799 |

800 |

801 | The command _____ can move or rename files and directories 802 |

803 | mv 804 |

805 | 806 |

807 |

808 | The directory /usr predominantly stores _____ 809 |

810 | Application files 811 |

812 | 813 |

814 |

815 | The command cp _____ 816 |

817 | original.txt copy.txt copies a file 818 |

819 | 820 |

821 |

822 | The command sdiff _____ 823 |

824 | merges two files interactively 825 |

826 | 827 |

828 |

829 | The command _____ can determine a file's type 830 |

831 | file 832 |

833 | 834 |

835 |

836 | The command ls -l _____ 837 |

838 | lists folders alphabetically 839 |

840 | 841 |

842 |

843 | The command _____ extracts a tar file 844 |

845 | tar -xf 846 |

847 | 848 |

849 |

850 | The command _____ creates new folders 851 |

852 | mkdir 853 |

854 | 855 |

856 |

857 | The command scp _____ 858 |

859 | makes a secure, remote file copy. 860 |

861 | 862 |

863 |

864 | The command cd _____ 865 |

866 | changes the current working directory 867 |

868 | 869 |

870 |

871 | Does a file's inode store its special attributes? _____ 872 |

873 | Yes 874 |

875 | 876 |

877 |

878 | The command whereis _____ 879 |

880 | searches for a program 881 |

882 | 883 |

884 |

885 | The command link _____ 886 |

887 | creates a link to a file 888 |

889 | 890 |

891 |

892 | The command grep _____ 893 |

894 | can search files for lines that match a pattern 895 |

896 | 897 |

898 |

899 | Does every directory have an inode? _____ 900 |

901 | Yes 902 |

903 | 904 |

905 |

906 | The command _____ prints the present working directory 907 |

908 | pwd 909 |

910 | 911 |

912 |

913 | The command _____ outputs the first line of a file 914 |

915 | head -1 file.txt 916 |

917 | 918 |

919 |

920 | The command _____ lists folders alphabetically 921 |

922 | ls -l 923 |

924 | 925 |

926 |

927 | The command _____ creates a link to a file 928 |

929 | link 930 |

931 | 932 |

933 |

934 | The command tail -1 file.txt _____ 935 |

936 | outputs the last line of a file 937 |

938 | 939 |

940 |

941 | Does a file's inode store its owner, group and permission information? _____ 942 |

943 | Yes 944 |

945 | 946 |

947 |

948 | The command ls -l _____ 949 |

950 | displays the long list of a folder 951 |

952 | 953 |

954 |

955 | The command cut _____ 956 |

957 | can divide a file into several parts 958 |

959 | 960 |

961 |

962 | The command _____ can redirect output towards multiple files 963 |

964 | tee 965 |

966 | 967 |

968 |

969 | The command ddrescue _____ 970 |

971 | helps recover data, especially after using dd 972 |

973 | 974 |

975 |

976 | The command _____ displays the long list of a folder 977 |

978 | ls -l 979 |

980 | 981 |

982 |

983 | Metadata about the filesystem (Type, Size, Mounts, Status) is called the _____ 984 |

985 | Superblock 986 |

987 | 988 |

989 |

990 | The command quotactl _____ 991 |

992 | scans a file system for disk usage 993 |

994 | 995 |

996 |

997 | The command _____ checks and repairs filesystem consistency 998 |

999 | fsck 1000 |

1001 | 1002 |

1003 |

1004 | The command _____ lists files in use by processes 1005 |

1006 | lsof 1007 |

1008 | 1009 |

1010 |

1011 | The command lsof _____ 1012 |

1013 | lists files in use by processes 1014 |

1015 | 1016 |

1017 |

1018 | The command _____ pipes an unsorted.txt file into the sort command 1019 |

1020 | sort < unsorted.txt 1021 |

1022 | 1023 |

1024 |

1025 | The command tail -F _____ 1026 |

1027 | continously prints newly added lines of a file 1028 |

1029 | 1030 |

1031 |

1032 | Does a file's inode store the number of links existing to the file? _____ 1033 |

1034 | Yes 1035 |

1036 | 1037 |

1038 |

1039 | The command dirname _____ 1040 |

1041 | can convert a full pathname to just a path 1042 |

1043 | 1044 |

1045 |

1046 | The command _____ gets a file's word count 1047 |

1048 | wc 1049 |

1050 | 1051 | -------------------------------------------------------------------------------- /docs/index.md: -------------------------------------------------------------------------------- 1 | # linux-faq 2 | 3 | Questions to test your Linux knowledge. 4 | 5 | ## Table of Contents: 6 | 7 | 1. [cgroups](https://katademy.github.io/linux-faq/cgrou[s]) 8 | 1. [devices](https://katademy.github.io/linux-faq/devices) 9 | 1. [files](https://katademy.github.io/linux-faq/files) 10 | 1. [namespaces](https://katademy.github.io/linux-faq/namespaces) 11 | 1. [network](https://katademy.github.io/linux-faq/network) 12 | 1. [processes](https://katademy.github.io/linux-faq/processes) 13 | 1. [security](https://katademy.github.io/linux-faq/security) 14 | 1. [shell](https://katademy.github.io/linux-faq/shell) 15 | 1. [signals](https://katademy.github.io/linux-faq/signals) 16 | 1. [syscalls](https://katademy.github.io/linux-faq/syscalls) 17 | 1. [system](https://katademy.github.io/linux-faq/system) 18 | 19 | #### Like this project? 20 | 21 | * [Leave a Star](https://github.com/katademy/linux-faq/stargazers) 22 | * Follow [@katademy](https://twitter.com/katademy) on Twitter 23 | * Donate via [PayPal](https://paypal.me/icelynjennings) or [Patreon](https://patreon.com/icelynjennings) 24 | -------------------------------------------------------------------------------- /docs/namespaces.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | Do namespaces provide processes with their own view of the system? _____ 4 |

5 | Yes 6 |

7 | 8 |

9 |

10 | Can namespaces isolate users per process? _____ 11 |

12 | Yes 13 |

14 | 15 |

16 |

17 | The available namespaces in Linux are, pid, net, _____, uts, ipc, user, time, cgroup 18 |

19 | mnt 20 |

21 | 22 |

23 |

24 | Can namespaces isolate networking per process? _____ 25 |

26 | Yes 27 |

28 | 29 |

30 |

31 | The available namespaces in Linux are, pid, net, mnt, uts, _____, user, time, cgroup 32 |

33 | ipc 34 |

35 | 36 |

37 |

38 | Processes within the _____ namespace can only see the other processes within it. 39 |

40 | PID 41 |

42 | 43 |

44 |

45 | The available namespaces in Linux are, pid, net, mnt, uts, ipc, user, time, _____ 46 |

47 | cgroup 48 |

49 | 50 |

51 |

52 | Can network namespaces communicate with each other via a bridge network? _____ 53 |

54 | Yes 55 |

56 | 57 |

58 |

59 | Does each PID namespace have its own numbering? _____ 60 |

61 | Yes 62 |

63 | 64 |

65 |

66 | The PID 1 namespace is removed from a PID namespace. What happens? _____ 67 |

68 | The PID namespace is destroyed 69 |

70 | 71 |

72 |

73 | Using _____ namespaces, you can improve security by giving a unique /tmp or /proc directories to every user. 74 |

75 | mnt 76 |

77 | 78 |

79 |

80 | Can namespaces isolate UTS per process? _____ 81 |

82 | Yes 83 |

84 | 85 |

86 |

87 | The available namespaces in Linux are, pid, _____, mnt, uts, ipc, user, time, cgroup 88 |

89 | net 90 |

91 | 92 |

93 |

94 | Can PID namespaces be nested? (namespace within namespace within namespace...) _____ 95 |

96 | Yes 97 |

98 | 99 |

100 |

101 | Namespaces are created with the _____ syscall. 102 |

103 | clone() 104 |

105 | 106 |

107 |

108 | A newly made process inherits its namespaces from the _____ process. 109 |

110 | parent 111 |

112 | 113 |

114 |

115 | The available namespaces in Linux are, pid, net, mnt, uts, ipc, _____, time, cgroup 116 |

117 | user 118 |

119 | 120 |

121 |

122 | The available namespaces in Linux are, _____, net, mnt, uts, ipc, user, time, cgroup 123 |

124 | pid 125 |

126 | 127 |

128 |

129 | Can namespaces isolate Inter-Process Communication per process? _____ 130 |

131 | Yes 132 |

133 | 134 |

135 |

136 | You can specify the mounted filesystems/devices visible to a process inside a _____ namespace. 137 |

138 | mount namespace 139 |

140 | 141 |

142 |

143 | Can process namespaces be used to isolate processes? _____ 144 |

145 | Yes 146 |

147 | 148 |

149 |

150 | An mnt namespace's mounts be _____ or shared 151 |

152 | private 153 |

154 | 155 |

156 |

157 | Can namespaces isolate mounts per process? _____ 158 |

159 | Yes 160 |

161 | 162 |

163 |

164 | Can namespaces isolate drives and devices per process? _____ 165 |

166 | Yes 167 |

168 | 169 |

170 |

171 | ______ allow processes to use identically named resources and isolate them. 172 |

173 | namespaces 174 |

175 | 176 |

177 |

178 | The /proc/[pid]/ns/ directory contains the process's _____ 179 |

180 | links to namespaces used by the process 181 |

182 | 183 |

184 |

185 | Using the _____ namespaces, processes can be given their own root filesystem (conceptually close to chroot) 186 |

187 | mnt 188 |

189 | 190 |

191 |

192 | How many namespaces of can a process simultaneously be in? _____ 193 |

194 | One of each type 195 |

196 | 197 |

198 |

199 | "When PID namespaces are nested inside one another, a process inside one has as many _____ as the namespace levels it is nested in. This is how features like """"docker in docker"""" can be implemented.""" 200 |

201 | PIDs 202 |

203 | 204 |

205 |

206 | "Network namespaces can use Virtual Ethernet (veth) pairs to communicate. This involves creating two _____ acting as a """"cross-over cable"""" between them.""" 207 |

208 | virtual network interfaces 209 |

210 | 211 |

212 |

213 | Can namespaces isolate hostnames per process? _____ 214 |

215 | Yes 216 |

217 | 218 |

219 |

220 | The available namespaces in Linux are, pid, net, mnt, uts, ipc, user, _____, cgroup 221 |

222 | time 223 |

224 | 225 |

226 |

227 | The command setns _____ 228 |

229 | adds a process to an existing namespace 230 |

231 | 232 |

233 |

234 | The available namespaces in Linux are, pid, net, mnt, _____, ipc, user, time, cgroup 235 |

236 | uts 237 |

238 | 239 |

240 |

241 | Can namespaces isolate PIDs per process? _____ 242 |

243 | Yes 244 |

245 | 246 |

247 |

248 | The command nsenter _____ 249 |

250 | enters a Linux namespace 251 |

252 | 253 |

254 |

255 | The _____ namespace allows processes to have their own semaphores, message queues and shared memory, without risk of conflict with other processes. 256 |

257 | IPC 258 |

259 | 260 |

261 |

262 | Can namespaces isolate resources per one or more processes? _____ 263 |

264 | Yes 265 |

266 | 267 |

268 |

269 | The _____ namespace allows you to map the UID/GID of processes. Even though you might be a privileged user with UID 0 in a container, you will just be user xxxxx on the host. 270 |

271 | user 272 |

273 | 274 |

275 |

276 | An mnt namespace's mounts be private or _____ 277 |

278 | shared 279 |

280 | 281 |

282 |

283 | The command ip link set dev eth0 netns ns0 _____ 284 |

285 | moves a network interface eth0 to namespace ns0 286 |

287 | 288 |

289 |

290 | The last process inside a namespace dies. What happens? _____ 291 |

292 | The namespace is destroyed. You can prevent this by creating a bind mount inside the namespace. 293 |

294 | 295 |

296 |

297 | The _____ namespace allows processes inside one to have their own network stack: sockets, iptables, routing tables and network interfaces (including loopback) 298 |

299 | net 300 |

301 | 302 |

303 |

304 | The command _____ moves a network interface eth0 to namespace ns0 305 |

306 | ip link set dev eth0 netns ns0 307 |

308 | 309 |

310 |

311 | A process is in a namespace. Which system resources can it see or affect? _____ 312 |

313 | Only those allowed in the namespace. 314 |

315 | 316 |

317 |

318 | The _____ namespace lets a container mount something, and make it invisible to other containers. 319 |

320 | mnt 321 |

322 | 323 |

324 |

325 | The command _____ enters a Linux namespace 326 |

327 | nsenter 328 |

329 | 330 |

331 |

332 | The command _____ adds a process to an existing namespace 333 |

334 | setns 335 |

336 | 337 |

338 |

339 | The _____ directory contains the process's links to namespaces used by the process 340 |

341 | /proc/[pid]/ns/ 342 |

343 | 344 | -------------------------------------------------------------------------------- /docs/network.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | The command _____ displays the status of the network 4 |

5 | netstat 6 |

7 | 8 |

9 |

10 | The command netstat _____ 11 |

12 | displays the status of the network 13 |

14 | 15 |

16 |

17 | Predefined ports used by the OS for short-lived client sockets are called _____ ports. 18 |

19 | Ephemeral 20 |

21 | 22 |

23 |

24 | The command ip link set veth1 netns ns1 _____ 25 |

26 | adds a virtual ethernet interface to a network namespace 27 |

28 | 29 |

30 |

31 | The command _____ creates a network namespace 32 |

33 | ip netns add ns1 34 |

35 | 36 |

37 |

38 | The command _____ traces the route to a given host 39 |

40 | traceroute 41 |

42 | 43 |

44 |

45 | The command ip link _____ 46 |

47 | lists network interfaces on the localhost 48 |

49 | 50 |

51 |

52 | The command ethtool _____ 53 |

54 | shows Ethernet card settings 55 |

56 | 57 |

58 |

59 | The command ip addr _____ 60 |

61 | shows network interfaces on the host system 62 |

63 | 64 |

65 |

66 | The command ip -n ns1 addr add 192.168.15.1 dev veth1 _____ ip -n ns1 link set veth1 up ip -n ns2 link set veth2 up assigns an IP to a network namespace 67 |

68 | ip -n ns2 addr add 192.168.15.2 dev veth2 69 |

70 | 71 |

72 |

73 | The command ip netns exec _____ 74 |

75 | can be used to run commands inside a network namespace 76 |

77 | 78 |

79 |

80 | The command _____ displays remote hosts connected to yours on port 3333 81 |

82 | netstat -a | grep 3333 83 |

84 | 85 |

86 |

87 | The _____ file is a list of hostname-to-IP address mappings for resolving hostnames (DNS) 88 |

89 | /etc/hosts 90 |

91 | 92 |

93 |

94 | The command nslookup _____ 95 |

96 | queries a website's name server 97 |

98 | 99 |

100 |

101 | The command _____ shows network interfaces on the host system 102 |

103 | ip addr 104 |

105 | 106 |

107 |

108 | To connect several network namespaces you need a virtual _____, ex. Linux Bridge or Open vSwitch 109 |

110 | switch / bridge network 111 |

112 | 113 |

114 |

115 | Can network namespaces (netns) implement network isolation? _____ 116 |

117 | Yes 118 |

119 | 120 |

121 |

122 | The command ip -n ns1 link _____ 123 |

124 | lists network interfaces inside a namespace 125 |

126 | 127 |

128 |

129 | The command _____ can be used to run commands inside a network namespace 130 |

131 | ip netns exec 132 |

133 | 134 |

135 |

136 | The command ip -n ns1 link del veth1 _____ 137 |

138 | deletes a veth pair between namespaces 139 |

140 | 141 |

142 |

143 | The command ip route add blackhole $BANNED_IP _____ 144 |

145 | blocks an IP from connecting to your host 146 |

147 | 148 |

149 |

150 | The tracert command uses the _____ network protocol 151 |

152 | ICMP 153 |

154 | 155 |

156 |

157 | The command ip link add veth1 type veth peer name veth2 _____ 158 |

159 | links two virtual ethernet interfaces 160 |

161 | 162 |

163 |

164 | The command _____ queries a website's name server 165 |

166 | nslookup 167 |

168 | 169 |

170 |

171 | The command traceroute _____ 172 |

173 | traces the route to a given host 174 |

175 | 176 |

177 |

178 | The command _____ links two virtual ethernet interfaces 179 |

180 | ip link add veth1 type veth peer name veth2 181 |

182 | 183 |

184 |

185 | The command _____ ip -n ns2 addr add 192.168.15.2 dev veth2 ip -n ns1 link set veth1 up ip -n ns2 link set veth2 up assigns an IP to a network namespace 186 |

187 | ip -n ns1 addr add 192.168.15.1 dev veth1 188 |

189 | 190 |

191 |

192 | The command ip -n ns1 addr add 192.168.15.1 dev veth1 ip -n ns2 addr add 192.168.15.2 dev veth2 ip -n ns1 link set veth1 up _____ assigns an IP to a network namespace 193 |

194 | ip -n ns2 link set veth2 up 195 |

196 | 197 |

198 |

199 | The command ip -n ns1 addr add 192.168.15.1 dev veth1 ip -n ns2 addr add 192.168.15.2 dev veth2 ip -n ns1 link set veth1 up ip -n ns2 link set veth2 up _____ 200 |

201 | assigns an IP to a network namespace 202 |

203 | 204 |

205 |

206 | The command ip netns add ns1 _____ 207 |

208 | creates a network namespace 209 |

210 | 211 |

212 |

213 | "The command ip link add veth1 type veth peer name veth1-bridge ip link set veth1-bridge master v-net-0 _____" 214 |

215 | links a veth interface ""veth1"" to a bridge network ""v-net-0"" 216 |

217 | 218 |

219 |

220 | The command _____ lists network interfaces on the localhost 221 |

222 | ip link 223 |

224 | 225 |

226 |

227 | The command _____ finds the hostname of an IP address. 228 |

229 | dig 230 |

231 | 232 |

233 |

234 | The _____ file specifies the DNS server and domain suffix of the system. 235 |

236 | /etc/resolv.conf 237 |

238 | 239 |

240 |

241 | The command ip -n ns1 addr add 192.168.15.1 dev veth1 ip -n ns2 addr add 192.168.15.2 dev veth2 _____ ip -n ns2 link set veth2 up assigns an IP to a network namespace 242 |

243 | ip -n ns1 link set veth1 up 244 |

245 | 246 |

247 |

248 | The command _____ blocks an IP from connecting to your host 249 |

250 | ip route add blackhole $BANNED_IP 251 |

252 | 253 |

254 |

255 | The command netstat -a | grep 3333 _____ 256 |

257 | displays remote hosts connected to yours on port 3333 258 |

259 | 260 |

261 |

262 | The command _____ lists network interfaces inside a namespace 263 |

264 | ip -n ns1 link 265 |

266 | 267 |

268 |

269 | "The command _____ links a veth interface ""veth1"" to a bridge network ""v-net-0""" 270 |

271 | ip link add veth1 type veth peer name veth1-bridge ip link set veth1-bridge master v-net-0 272 |

273 | 274 |

275 |

276 | The command dig _____ 277 |

278 | finds the hostname of an IP address. 279 |

280 | 281 |

282 |

283 | The command _____ creates a new bridge network 284 |

285 | ip link add v-net-0 type bridge ip link set dev v-net-0 up 286 |

287 | 288 |

289 |

290 | The command _____ adds a virtual ethernet interface to a network namespace 291 |

292 | ip link set veth1 netns ns1 293 |

294 | 295 |

296 |

297 | The ping command uses the _____ network protocol 298 |

299 | ICMP 300 |

301 | 302 |

303 |

304 | The command ip link add v-net-0 type bridge ip link set dev v-net-0 up _____ 305 |

306 | creates a new bridge network 307 |

308 | 309 |

310 |

311 | The command _____ deletes a veth pair between namespaces 312 |

313 | ip -n ns1 link del veth1 314 |

315 | 316 |

317 |

318 | The command _____ shows Ethernet card settings 319 |

320 | ethtool 321 |

322 | 323 | -------------------------------------------------------------------------------- /docs/processes.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | named pipes are FIFO files creatable with mkfifo which allow communication between two _____ on the same host. Network sockets / local domain sockets have mostly superseded them. 4 |

5 | processes 6 |

7 | 8 |

9 |

10 | Can processes communicate via sockets? _____ 11 |

12 | Yes 13 |

14 | 15 |

16 |

17 | The command _____ show process status 18 |

19 | ps 20 |

21 | 22 |

23 |

24 | The command _____ sends a job to the foreground 25 |

26 | fg 27 |

28 | 29 |

30 |

31 | The directory _____ predominantly stores Processes. The directory is a psuedo-filesystem, dynamically created whenever it is accessed 32 |

33 | /proc 34 |

35 | 36 |

37 |

38 | init (or systemd) is the process with PID _____ that executes system startup scripts. 39 |

40 | 1 41 |

42 | 43 |

44 |

45 | The file /proc/[pid]/stat contains _____ 46 |

47 | the process's status information (decoded by the ps command) 48 |

49 | 50 |

51 |

52 | Each process has one or several execution contexts called _____, each with its own stack and CPU context, but the exact same address space as their process 53 |

54 | threads 55 |

56 | 57 |

58 |

59 | When you run the command ls: 1. Your input gets read by the shell via getline(). 2. The name is found within your $PATH directories. 3. The clone() _____ duplicates the process, giving the child a new PID. 4. The execve() _____ stops the child and replaces its memory stack with data from the ls binary. 5. The parent process runs wait(), as it will clean after the child process when finished 60 |

61 | syscall 62 |

63 | 64 |

65 |

66 | The command _____ shows processes of all users 67 |

68 | ps -a 69 |

70 | 71 |

72 |

73 | A process's _____ determinates how much CPU time it receives 74 |

75 | scheduling priority 76 |

77 | 78 |

79 |

80 | "When a process is cloned, we call the original process the ""_____"", and we call the clone the ""child""" 81 |

82 | parent 83 |

84 | 85 |

86 |

87 | The file _____ contains the process's command it's executing 88 |

89 | /proc/[pid]/cmd 90 |

91 | 92 |

93 |

94 | The command _____ shows processes along with their user/owner 95 |

96 | ps -u 97 |

98 | 99 |

100 |

101 | All other processes are directly or indirectly the children of _____ 102 |

103 | The PID 1 process (init or systemd) 104 |

105 | 106 |

107 |

108 | The command ps -x _____ 109 |

110 | shows procceses unattached to any terminal 111 |

112 | 113 |

114 |

115 | Cron's asterisk (* * * * *) syntax denotes, in order: minute, hour, _____, weekday 116 |

117 | day of the month 118 |

119 | 120 |

121 |

122 | When you run the command ls: 1. Your input gets read by the shell via getline(). 2. The name is found within your _____. 3. The clone() syscall duplicates the process, giving the child a new PID. 4. The execve() syscall stops the child and replaces its memory stack with data from the ls binary. 5. The parent process runs wait(), as it will clean after the child process when finished 123 |

124 | $PATH directories 125 |

126 | 127 |

128 |

129 | The crontab command schedules processes at regular intervals. The cron _____ executes and logs them 130 |

131 | daemon 132 |

133 | 134 |

135 |

136 | The command fuser _____ 137 |

138 | identifies the process that is accessing a file 139 |

140 | 141 |

142 |

143 | The command jobs _____ 144 |

145 | lists active jobs 146 |

147 | 148 |

149 |

150 | The file _____ contains the process's memory mapping information 151 |

152 | /proc/[pid]/maps 153 |

154 | 155 |

156 |

157 | The file _____ contains the process's complete command line 158 |

159 | /proc/[pid]/cmdline 160 |

161 | 162 |

163 |

164 | The file /proc/[pid]/cmdline contains _____ 165 |

166 | the process's complete command line 167 |

168 | 169 |

170 |

171 | Cron's asterisk (* * * * *) syntax denotes, in order: minute, _____, day of the month, weekday 172 |

173 | hour 174 |

175 | 176 |

177 |

178 | Cron's asterisk (* * * * *) syntax denotes, in order: minute, hour, day of the month, _____ 179 |

180 | weekday 181 |

182 | 183 |

184 |

185 | After a clone(), child processes usually run one of the _____ routines, replacing the process they've copied from their parent 186 |

187 | exec() 188 |

189 | 190 |

191 |

192 | The command setuid _____ 193 |

194 | manipulates a process' UID 195 |

196 | 197 |

198 |

199 | The file _____ contains the process's symbolic link to its current directory 200 |

201 | /proc/[pid]/cwd 202 |

203 | 204 |

205 |

206 | The file /proc/[pid]/maps contains the process's _____ 207 |

208 | memory mapping information 209 |

210 | 211 |

212 |

213 | The file /proc/[pid]/statm contains the process's _____ 214 |

215 | memory usage info 216 |

217 | 218 |

219 |

220 | _____ are programs running indefinitely in the background 221 |

222 | daemons 223 |

224 | 225 |

226 |

227 | A process consists of an address space and a set of data structures in the _____ 228 |

229 | kernel 230 |

231 | 232 |

233 |

234 | The command _____ prints the process tree of a process 235 |

236 | pstree -p [PID] 237 |

238 | 239 |

240 |

241 | Are PID's (process ID's) unique? _____ 242 |

243 | Yes 244 |

245 | 246 |

247 |

248 | The command setgid _____ 249 |

250 | manipulates a process's group 251 |

252 | 253 |

254 |

255 | The crontab command _____. The cron daemon executes and logs them 256 |

257 | schedules processes at regular intervals 258 |

259 | 260 |

261 |

262 | The crontab command schedules processes at regular intervals. The _____ daemon executes and logs them 263 |

264 | cron 265 |

266 | 267 |

268 |

269 | The command kill (without flags) sends the SIGTERM signal to a process. SIGTERM may not necessarily terminate the process, as this particular signal be either caught, _____ or ignored by the process. 270 |

271 | blocked 272 |

273 | 274 |

275 |

276 | When you run the command ls: 1. Your input gets read by the shell via getline(). 2. The name is found within your $PATH directories. 3. The clone() syscall duplicates the process, giving the child a new PID. 4. The _____ syscall stops the child and replaces its memory stack with data from the ls binary. 5. The parent process runs wait(), as it will clean after the child process when finished 277 |

278 | execve() 279 |

280 | 281 |

282 |

283 | Each process has one or several execution contexts called threads, each with its own stack and CPU context, but the exact same _____ as their process 284 |

285 | address space 286 |

287 | 288 |

289 |

290 | Each process has one or several execution contexts called threads, each with its own stack and _____, but the exact same address space as their process 291 |

292 | CPU context 293 |

294 | 295 |

296 |

297 | After a _____, child processes usually run one of the exec() routines, replacing the process they've copied from their parent 298 |

299 | clone() 300 |

301 | 302 |

303 |

304 | Before a dead process disappears, its death must be acknowledged by _____, who does so with a call to wait() 305 |

306 | its parent 307 |

308 | 309 |

310 |

311 | The file _____ contains the process's environment variables 312 |

313 | /proc/[pid]/environ 314 |

315 | 316 |

317 |

318 | The file _____ contains the process's memory usage info 319 |

320 | /proc/[pid]/statm 321 |

322 | 323 |

324 |

325 | The command _____ manipulates a process's group 326 |

327 | setgid 328 |

329 | 330 |

331 |

332 | A file is being read in a thread. The kernel requests the file's content be delivered into the requesting process's address space. Until it finishes, the thread is considered _____. 333 |

334 | sleeping 335 |

336 | 337 |

338 |

339 | Local domain sockets are connections between processes on the same host, creatable with the ______ system call. 340 |

341 | socket 342 |

343 | 344 |

345 |

346 | Which Linux syscalls create a new process? _____ 347 |

348 | clone() copies an existing process, whose running command is replaced to a desired new command via exec() 349 |

350 | 351 |

352 |

353 | The command _____ limits the use of system-wide resources for a user 354 |

355 | ulimit 356 |

357 | 358 |

359 |

360 | A process's scheduling priority determinates how much _____ it receives 361 |

362 | CPU time 363 |

364 | 365 |

366 |

367 | Can processes communicate via named pipes? _____ 368 |

369 | Yes 370 |

371 | 372 |

373 |

374 | The file _____ contains the process's status information (decoded by the ps command) 375 |

376 | /proc/[pid]/stat 377 |

378 | 379 |

380 |

381 | The file /proc/[pid]/cwd contains the process's _____ 382 |

383 | symbolic link to its current directory 384 |

385 | 386 |

387 |

388 | The GID is the numeric identificator for a process's _____ 389 |

390 | group 391 |

392 | 393 |

394 |

395 | "When a process is cloned, we call the original process the ""parent"", and we call the clone the ""_____""" 396 |

397 | child 398 |

399 | 400 |

401 |

402 | Can processes communicate via anonymous pipes? _____ 403 |

404 | Yes 405 |

406 | 407 |

408 |

409 | Cron's _____ syntax denotes, in order: minute, hour, day of the month, weekday 410 |

411 | asterisk (* * * * *) 412 |

413 | 414 |

415 |

416 | Before a dead process disappears, its death must be acknowledged by its parent, who does so with a call to _____ 417 |

418 | wait() 419 |

420 | 421 |

422 |

423 | The command kill (without flags) sends the _____ signal to a process. _____ may not necessarily terminate the process, as this particular signal be either caught, blocked or ignored by the process. 424 |

425 | SIGTERM 426 |

427 | 428 |

429 |

430 | The command ps -u _____ 431 |

432 | shows processes along with their user/owner 433 |

434 | 435 |

436 |

437 | A _____ is the abstraction memory, processor time, I/O management and monitoring for a single running program 438 |

439 | Process 440 |

441 | 442 |

443 |

444 | Do threads share the stack and CPU context with their process? _____ 445 |

446 | No 447 |

448 | 449 |

450 |

451 | When you run the command ls: 1. Your input gets read by the shell via getline(). 2. The name is found within your $PATH directories. 3. The _____ syscall duplicates the process, giving the child a new PID. 4. The execve() syscall stops the child and replaces its memory stack with data from the ls binary. 5. The parent process runs wait(), as it will clean after the child process when finished 452 |

453 | clone() 454 |

455 | 456 |

457 |

458 | The file /proc/[pid]/environ contains the process's _____ 459 |

460 | environment variables 461 |

462 | 463 |

464 |

465 | The file _____ contains the process's symbolic link to its root directory (set via chroot) 466 |

467 | /proc/[pid]/root 468 |

469 | 470 |

471 |

472 | The command _____ is the modern version of fork that handles threads 473 |

474 | clone() 475 |

476 | 477 |

478 |

479 | A process' _____ is a set of memory pages that the kernel has marked for the procesS to use 480 |

481 | address space 482 |

483 | 484 |

485 |

486 | The command pstree -p [PID] _____ 487 |

488 | prints the process tree of a process 489 |

490 | 491 |

492 |

493 | The command renice _____ 494 |

495 | changes the priority of a running process 496 |

497 | 498 |

499 |

500 | The command _____ displays processes in a user oriented format 501 |

502 | ps -u 503 |

504 | 505 |

506 |

507 | UTS stands for _____ and it gives a container its own hostname and domain name 508 |

509 | Unix Timesharing System 510 |

511 | 512 |

513 |

514 | The command ps -a _____ 515 |

516 | shows processes of all users 517 |

518 | 519 |

520 |

521 | The command _____ changes the priority of a running process 522 |

523 | renice 524 |

525 | 526 |

527 |

528 | The command _____ shows a real-time, interactive list of processes 529 |

530 | top 531 |

532 | 533 |

534 |

535 | A parent process has died before it could clean up its child processes via a call to _____. What happens to the child processes? The PID 1 process (usually init or systemd) adopts them and calls wait 536 |

537 | wait 538 |

539 | 540 |

541 |

542 | The command top _____ 543 |

544 | shows a real-time, interactive list of processes 545 |

546 | 547 |

548 |

549 | The command _____ (without flags) sends the SIGTERM signal to a process. SIGTERM may not necessarily terminate the process, as this particular signal be either caught, blocked or ignored by the process. 550 |

551 | kill 552 |

553 | 554 |

555 |

556 | The command ps _____ 557 |

558 | show process status 559 |

560 | 561 |

562 |

563 | The _____ directory contains the process's information on open file descriptors 564 |

565 | /proc/[pid]/fdinfo/ 566 |

567 | 568 |

569 |

570 | The command kill (without flags) sends the _____ signal to a process. _____ may not necessarily terminate the process, as this particular signal be either caught, blocked or ignored by the process. 571 |

572 | SIGTERM 573 |

574 | 575 |

576 |

577 | The file /proc/[pid]/root contains the process's _____ 578 |

579 | symbolic link to its root directory (set via chroot) 580 |

581 | 582 |

583 |

584 | Jobs are identified by their _____ and JID (Job ID) 585 |

586 | PID (Process ID) 587 |

588 | 589 |

590 |

591 | The /proc/[pid]/fdinfo/ directory contains the process's _____ 592 |

593 | information on open file descriptors 594 |

595 | 596 |

597 |

598 | The clone() syscall returns two values. To the parent it returns the PID of the new child. To the child it returns _____. This informs them both of what role they are playing in the forking 599 |

600 | 0 601 |

602 | 603 |

604 |

605 | The _____ command schedules processes at regular intervals. The cron daemon executes and logs them 606 |

607 | crontab 608 |

609 | 610 |

611 |

612 | The higher the niceness of a process, the _____ priority it has. 613 |

614 | lower 615 |

616 | 617 |

618 |

619 | Cron's asterisk (* * * * *) syntax denotes, in order: _____, hour, day of the month, weekday 620 |

621 | minute 622 |

623 | 624 |

625 |

626 | Can processes communicate via SysV queues? _____ 627 |

628 | Yes 629 |

630 | 631 |

632 |

633 | daemons are _____ 634 |

635 | programs running indefinitely in the background 636 |

637 | 638 |

639 |

640 | The command _____ shows procceses unattached to any terminal 641 |

642 | ps -x 643 |

644 | 645 |

646 |

647 | The file /proc/exe contains the process's _____ 648 |

649 | symbolic link to the executed file 650 |

651 | 652 |

653 |

654 | The command _____ inversely sets the priority of a process (the lower the niceness, the higher the priority) 655 |

656 | nice 657 |

658 | 659 |

660 |

661 | Can processes communicate via D-Bus? _____ 662 |

663 | Yes 664 |

665 | 666 |

667 |

668 | The command fg _____ 669 |

670 | sends a job to the foreground 671 |

672 | 673 |

674 |

675 | The directory /proc predominantly stores Processes. The directory is a psuedo-filesystem, _____ 676 |

677 | dynamically created whenever it is accessed 678 |

679 | 680 |

681 |

682 | Can processes communicate via SysV semaphores? _____ 683 |

684 | Yes 685 |

686 | 687 |

688 |

689 | Can processes communicate via SysV shared memory? _____ 690 |

691 | Yes 692 |

693 | 694 |

695 |

696 | The command ulimit _____ 697 |

698 | limits the use of system-wide resources for a user 699 |

700 | 701 |

702 |

703 | A process' address space is _____ 704 |

705 | a set of memory pages that the kernel has marked for the procesS to use 706 |

707 | 708 |

709 |

710 | The file /proc/[pid]/cmd contains _____ 711 |

712 | the process's command it's executing 713 |

714 | 715 |

716 |

717 | The command _____ manipulates a process' UID 718 |

719 | setuid 720 |

721 | 722 |

723 |

724 | A process' _____ is the user identification number (inherited from the parent process) of the user who created it. Usually, only the creator of a process, and the superuser, can manipulate the process. 725 |

726 | UID 727 |

728 | 729 |

730 |

731 | named pipes are FIFO files creatable with _____ which allow communication between two processes on the same host. Network sockets / local domain sockets have mostly superseded them. 732 |

733 | mkfifo 734 |

735 | 736 |

737 |

738 | A process' _____ contain variables, code, libraries, stacks and kernel-specific information that the process needs to execute 739 |

740 | address space memory pages 741 |

742 | 743 |

744 |

745 | When you run the command ls: 1. Your input gets read by the shell via getline(). 2. The name is found within your $PATH directories. 3. The clone() syscall duplicates the process, giving the child a new PID. 4. The execve() syscall stops the child and replaces its memory stack with data from the ls binary. 5. The parent process runs _____, as it will clean after the child process when finished 746 |

747 | wait() 748 |

749 | 750 |

751 |

752 | A parent process has died before it could clean up its child processes via a call to wait. What happens to the child processes? _____ 753 |

754 | The PID 1 process (usually init or systemd) adopts them and calls wait 755 |

756 | 757 |

758 |

759 | The file _____ contains the process's symbolic link to the executed file 760 |

761 | /proc/exe 762 |

763 | 764 |

765 |

766 | The clone() syscall returns two values. To the parent it returns _____. To the child it returns 0. This informs them both of what role they are playing in the forking 767 |

768 | the PID of the new child 769 |

770 | 771 |

772 |

773 | Can processes communicate via FIFO pipes? _____ 774 |

775 | Yes 776 |

777 | 778 |

779 |

780 | When you run the command ls: 1. Your input gets read by the shell via getline(). 2. The name is found within your $PATH directories. 3. The clone() _____ duplicates the process, giving the child a new PID. 4. The execve() _____ stops the child and replaces its memory stack with data from the ls binary. 5. The parent process runs wait(), as it will clean after the child process when finished 781 |

782 | syscall 783 |

784 | 785 |

786 |

787 | Upon a process's death, does its parent receive a copy of the exit code? _____ 788 |

789 | Yes 790 |

791 | 792 |

793 |

794 | The _____ of a child process refers to the PID of the process from which it was cloned. 795 |

796 | PPID 797 |

798 | 799 |

800 |

801 | The command kill (without flags) sends the SIGTERM signal to a process. SIGTERM may not necessarily terminate the process, as this particular signal be either caught, blocked or _____ by the process. 802 |

803 | ignored 804 |

805 | 806 |

807 |

808 | A process's place in the _____ contains its function parameters, local variables, return addresses and temporary data 809 |

810 | stack 811 |

812 | 813 |

814 |

815 | the _____ syscall creates a copy of the original process, with a new PID 816 |

817 | clone() 818 |

819 | 820 |

821 |

822 | A file is being read in a thread. The kernel requests the file's content be delivered into the requesting process's _____. Until it finishes, the thread is considered sleeping. 823 |

824 | address space 825 |

826 | 827 |

828 |

829 | _____ are FIFO files creatable with mkfifo which allow communication between two processes on the same host. Network sockets / local domain sockets have mostly superseded them. 830 |

831 | named pipes 832 |

833 | 834 |

835 |

836 | A process consists of an _____ and a set of data structures in the kernel 837 |

838 | address space 839 |

840 | 841 |

842 |

843 | When a process completes, it calls the exit routine, notifying the kernel that it is ready to be die, along with an integer _____ indicating the reason why 844 |

845 | exit code 846 |

847 | 848 |

849 |

850 | Processes that have finished execution but had not yet been cleaned up by their parent are called _____ processes. 851 |

852 | zombie 853 |

854 | 855 |

856 |

857 | The command nice _____ 858 |

859 | inversely sets the priority of a process (the lower the niceness, the higher the priority) 860 |

861 | 862 |

863 |

864 | The command _____ identifies the process that is accessing a file 865 |

866 | fuser 867 |

868 | 869 |

870 |

871 | When a process completes, it calls the _____ routine, notifying the kernel that it is ready to be die, along with an integer exit code indicating the reason why 872 |

873 | exit 874 |

875 | 876 |

877 |

878 | The command ps -u _____ 879 |

880 | displays processes in a user oriented format 881 |

882 | 883 |

884 |

885 | Do threads share the same address space as their process? _____ 886 |

887 | Yes 888 |

889 | 890 |

891 |

892 | The command kill (without flags) sends the SIGTERM signal to a process. SIGTERM may not necessarily terminate the process, as this particular signal be either _____, blocked or ignored by the process. 893 |

894 | caught 895 |

896 | 897 |

898 |

899 | The _____ is the numeric identificator for a process's group 900 |

901 | GID 902 |

903 | 904 |

905 |

906 | _____ are a soft limit on containers - the more of them a container has, the more prioritized it is by a scheduler 907 |

908 | CPU shares 909 |

910 | 911 |

912 |

913 | The command _____ lists active jobs 914 |

915 | jobs 916 |

917 | 918 |

919 |

920 | When you run the command ls: 1. Your input gets read by the shell via _____ 2. The name is found within your $PATH directories. 3. The clone() syscall duplicates the process, giving the child a new PID. 4. The execve() syscall stops the child and replaces its memory stack with data from the ls binary. 5. The parent process runs wait(), as it will clean after the child process when finished 921 |

922 | getline(). 923 |

924 | 925 |

926 |

927 | Jobs are identified by their PID (Process ID) and _____ 928 |

929 | JID (Job ID) 930 |

931 | 932 |

933 |

934 | The command clone() _____ 935 |

936 | is the modern version of fork that handles threads 937 |

938 | 939 |

940 |

941 | "A process is considered """"asleep"""" when _____""" 942 |

943 | All of its threads are asleep (i.e. waiting for the kernel to finish something for them, like reading contents of a file) 944 |

945 | 946 |

947 |

948 | The file _____ directory contains the process's links to open file descriptors 949 |

950 | /proc/[pid]/fd/ 951 |

952 | 953 |

954 |

955 | Each process has one or several execution contexts called threads, each with its own _____ and CPU context, but the exact same address space as their process 956 |

957 | stack 958 |

959 | 960 |

961 |

962 | The file /proc/[pid]/fd/ directory contains the process's _____ 963 |

964 | links to open file descriptors 965 |

966 | 967 | -------------------------------------------------------------------------------- /docs/security.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | The command useradd _____ 4 |

5 | creates a new user account. 6 |

7 | 8 |

9 |

10 | The command _____ changes a file's owner or group. 11 |

12 | chown 13 |

14 | 15 |

16 |

17 | The command _____ changes a user's password. 18 |

19 | passwd 20 |

21 | 22 |

23 |

24 | Default shell files should have default value of _____ set, for example to 077 25 |

26 | umask 27 |

28 | 29 |

30 |

31 | Debian's password encryption algorithm is set by Pluggable Authentication Modules (PAM) in the _____ file 32 |

33 | /etc/pam.d/common-passwd 34 |

35 | 36 |

37 |

38 | Encrypted Linux passwords all have the same _____, even if the unencrypted passwords do not 39 |

40 | length 41 |

42 | 43 |

44 |

45 | the chmod _____ permission means READ permission for owner, group and public 46 |

47 | 0444 48 |

49 | 50 |

51 |

52 | The command _____ modifies a group 53 |

54 | groupmod 55 |

56 | 57 |

58 |

59 | The command _____ modifies a user account. 60 |

61 | usermod 62 |

63 | 64 |

65 |

66 | gVisor is a _____ that can sandbox syscalls in userspace via restricted seccomp filters 67 |

68 | kernel security module 69 |

70 | 71 |

72 |

73 | The /etc/passwd file stores _____ 74 |

75 | users and data about them 76 |

77 | 78 |

79 |

80 | The _____ file contains group definitions. 81 |

82 | /etc/group 83 |

84 | 85 |

86 |

87 | the chmod 0111 permission means EXECUTE permission for _____ 88 |

89 | owner, group and public 90 |

91 | 92 |

93 |

94 | Login names can never contain colons or newlines - these characters are used as field and entry separators in the _____ file respectively 95 |

96 | /etc/passwd 97 |

98 | 99 |

100 |

101 | Each line of the /etc/shadow password file represents a user. The user's fields are separated by colons: username:password:Last password change:Minimum days required between password changes:_____:password expiration warning duration:password expiration ban deadline:{{c10::account expiration date}} 102 |

103 | Maximum days between password changes 104 |

105 | 106 |

107 |

108 | _____ filters decide which syscalls are allowed inside in a system. This prevents signals from being arbitrarily ran by an attacker, or being used to break out of a Linux namespace via unshare 109 |

110 | seccomp 111 |

112 | 113 |

114 |

115 | The root, system, or wheel group always has GID of _____ 116 |

117 | 0 118 |

119 | 120 |

121 |

122 | AppArmor profiles in complain mode _____ 123 |

124 | report violations 125 |

126 | 127 |

128 |

129 | Each line in the /etc/passwd file represents a user. A line's colon-separated fields represent: _____:password:UID:Default GID:comments:home:shell 130 |

131 | username 132 |

133 | 134 |

135 |

136 | AppArmor profiles in _____ mode block access to disallowed resources 137 |

138 | enforcing 139 |

140 | 141 |

142 |

143 | Each line of the /etc/shadow password file represents a user. The user's fields are separated by colons: _____:password:Last password change:Minimum days required between password changes:Maximum days between password changes:password expiration warning duration:password expiration ban deadline:{{c10::account expiration date}} 144 |

145 | username 146 |

147 | 148 |

149 |

150 | The command _____ sets a password for a user 151 |

152 | passwd [username] 153 |

154 | 155 |

156 |

157 | The command _____ reconciles the contents of the /etc/shadow and /etc/passwd files 158 |

159 | pwconv 160 |

161 | 162 |

163 |

164 | root user's UID always equals _____ 165 |

166 | 0 167 |

168 | 169 |

170 |

171 | the chmod 0444 permission means _____ permission for owner, group and public 172 |

173 | READ 174 |

175 | 176 |

177 |

178 | The command _____ sets a group's password, allowing users to enter it 179 |

180 | gpasswd 181 |

182 | 183 |

184 |

185 | RHEL's password encryption algorithm is set in the /etc/login.defs file, or through the _____ command 186 |

187 | authconfig 188 |

189 | 190 |

191 |

192 | The command _____ can change a user’s configuration through editing the /etc/passwd file 193 |

194 | vipw 195 |

196 | 197 |

198 |

199 | Each line of the /etc/shadow password file represents a user. The user's fields are separated by colons: username:password:Last password change:Minimum days required between password changes:Maximum days between password changes:password expiration warning duration:_____:{{c10::account expiration date}} 200 |

201 | password expiration ban deadline 202 |

203 | 204 |

205 |

206 | seccomp filters decide which _____ are allowed inside in a system. This prevents signals from being arbitrarily ran by an attacker, or being used to break out of a Linux namespace via unshare 207 |

208 | syscalls 209 |

210 | 211 |

212 |

213 | Debian's password encryption algorithm is set by _____ in the /etc/pam.d/common-passwd file 214 |

215 | Pluggable Authentication Modules (PAM) 216 |

217 | 218 |

219 |

220 | the chmod 0111 permission means _____ permission for owner, group and public 221 |

222 | EXECUTE 223 |

224 | 225 |

226 |

227 | The command userdel _____ 228 |

229 | deletes a user account. 230 |

231 | 232 |

233 |

234 | Each line of the /etc/shadow password file represents a user. The user's fields are separated by colons: username:password:_____:Minimum days required between password changes:Maximum days between password changes:password expiration warning duration:password expiration ban deadline:{{c10::account expiration date}} 235 |

236 | Last password change 237 |

238 | 239 |

240 |

241 | Each line in the /etc/passwd file represents a user. A line's colon-separated fields represent: username:password:UID:Default GID:comments:home:_____ 242 |

243 | shell 244 |

245 | 246 |

247 |

248 | Each line in the /etc/passwd file represents a user. A line's colon-separated fields represent: username:password:UID:Default GID:comments:_____:shell 249 |

250 | home 251 |

252 | 253 |

254 |

255 | Pseudo-users have a _____, and therefore cannot be logged into. They are commonly defined as owners of commands and configuration files 256 |

257 | fake login shell 258 |

259 | 260 |

261 |

262 | _____ is a kernel security module that confines programs to a limited set of resources, reducing an application's attack surface 263 |

264 | AppArmor 265 |

266 | 267 |

268 |

269 | The /etc/shadow password file is readable only by _____ 270 |

271 | the superuser 272 |

273 | 274 |

275 |

276 | "The command _____ searches the /var/log/ directory for usages of the word ""login""" 277 |

278 | grep login /var/log/* 279 |

280 | 281 |

282 |

283 | Each line of the /etc/shadow password file represents a user. The user's fields are separated by colons: username:password:Last password change:Minimum days required between password changes:Maximum days between password changes:_____:password expiration ban deadline:{{c10::account expiration date}} 284 |

285 | password expiration warning duration 286 |

287 | 288 |

289 |

290 | sh reads _____ before reading ~/.profile and ~/.bash_profile 291 |

292 | /etc/profile 293 |

294 | 295 |

296 |

297 | the chmod 0222 permission means _____ permission for owner, group and public 298 |

299 | WRITE 300 |

301 | 302 |

303 |

304 | Never manually edit /etc/passwd, /etc/group or /etc/shadow. Use the commands useradd, adduser, usermod, _____, vipw, vipw -s and chsh instead 305 |

306 | pw 307 |

308 | 309 |

310 |

311 | Are login names case-sensitive? _____ 312 |

313 | Yes 314 |

315 | 316 |

317 |

318 | The command _____ deletes a user account. 319 |

320 | userdel 321 |

322 | 323 |

324 |

325 | Human user UIDs should equal to _____ 326 |

327 | 1000 or higher 328 |

329 | 330 |

331 |

332 | A user's group memberships equals the union of those defined for the user in /etc/passwd and _____ 333 |

334 | /etc/group 335 |

336 | 337 |

338 |

339 | gVisor is a kernel security module that can _____ syscalls in userspace via restricted seccomp filters 340 |

341 | sandbox 342 |

343 | 344 |

345 |

346 | AppArmor profiles configure access to capabilities, network access, file permissions, either in _____ or complain mode 347 |

348 | enforcing 349 |

350 | 351 |

352 |

353 | The _____ file stores users and data about them 354 |

355 | /etc/passwd 356 |

357 | 358 |

359 |

360 | Never manually edit /etc/passwd, /etc/group or /etc/shadow. Use the commands useradd, _____, usermod, pw, vipw, vipw -s and chsh instead 361 |

362 | adduser 363 |

364 | 365 |

366 |

367 | The command chown _____ 368 |

369 | changes a file's owner or group. 370 |

371 | 372 |

373 |

374 | A Linux user is represented by its number: the _____ 375 |

376 | user ID or UID 377 |

378 | 379 |

380 |

381 | A user's group memberships equals the union of those defined for the user in _____ and /etc/group 382 |

383 | /etc/passwd 384 |

385 | 386 |

387 |

388 | The command passwd _____ 389 |

390 | changes a user's password. 391 |

392 | 393 |

394 |

395 | New files are typically owned by the user's _____ group 396 |

397 | effective 398 |

399 | 400 |

401 |

402 | Edit /etc/group by running _____ and /etc/gshadow by running vigr -s 403 |

404 | vigr 405 |

406 | 407 |

408 |

409 | Do login names have to be unique? _____ 410 |

411 | Yes 412 |

413 | 414 |

415 |

416 | Each line in the /etc/passwd file represents a _____. A line's colon-separated fields represent: username:password:UID:Default GID:comments:home:shell 417 |

418 | user 419 |

420 | 421 |

422 |

423 | The command whoami displays _____ 424 |

425 | the currently logged in user 426 |

427 | 428 |

429 |

430 | Group names should be limited to _____ characters for compatibility 431 |

432 | 8 433 |

434 | 435 |

436 |

437 | AppArmor profiles in enforcing mode _____ 438 |

439 | block access to disallowed resources 440 |

441 | 442 |

443 |

444 | The _____ password file is readable only by the superuser 445 |

446 | /etc/shadow 447 |

448 | 449 |

450 |

451 | A line in the /etc/group file represents a single group. Its fields are separated by colons: Name:Password:GID:_____ 452 |

453 | Members, separated by commas 454 |

455 | 456 |

457 |

458 | Each line in the /etc/passwd file represents a user. A line's colon-separated fields represent: username:password:UID:_____:comments:home:shell 459 |

460 | Default GID 461 |

462 | 463 |

464 |

465 | The command _____ displays the groups a user belongs to 466 |

467 | groups 468 |

469 | 470 |

471 |

472 | Never manually edit /etc/passwd, /etc/group or /etc/shadow. Use the commands _____, adduser, usermod, pw, vipw, vipw -s and chsh instead 473 |

474 | useradd 475 |

476 | 477 |

478 |

479 | AppArmor profiles configure access to capabilities, network access, file permissions, either in enforcing or _____ mode 480 |

481 | complain 482 |

483 | 484 |

485 |

486 | Each line in the /etc/passwd file represents a user. A line's colon-separated fields represent: username:password:_____:Default GID:comments:home:shell 487 |

488 | UID 489 |

490 | 491 |

492 |

493 | Each line of the /etc/shadow password file represents a user. The user's fields are separated by colons: username:_____:Last password change:Minimum days required between password changes:Maximum days between password changes:password expiration warning duration:password expiration ban deadline:{{c10::account expiration date}} 494 |

495 | password 496 |

497 | 498 |

499 |

500 | The command usermod _____ 501 |

502 | modifies a user account. 503 |

504 | 505 |

506 |

507 | The command id displays _____ 508 |

509 | user and group ID's 510 |

511 | 512 |

513 |

514 | Never manually edit /etc/passwd, /etc/group or /etc/shadow. Use the commands useradd, adduser, usermod, pw, _____, vipw -s and chsh instead 515 |

516 | vipw 517 |

518 | 519 |

520 |

521 | the chmod _____ permission means EXECUTE permission for owner, group and public 522 |

523 | 0111 524 |

525 | 526 |

527 |

528 | AppArmor _____ configure access to capabilities, network access, file permissions, either in enforcing or complain mode 529 |

530 | profiles 531 |

532 | 533 |

534 |

535 | The command _____ adds a user group 536 |

537 | groupadd 538 |

539 | 540 |

541 |

542 | The /etc/shadow file contains _____ 543 |

544 | encrypted passwords. 545 |

546 | 547 |

548 |

549 | _____ profiles configure access to capabilities, network access, file permissions, either in enforcing or complain mode 550 |

551 | AppArmor 552 |

553 | 554 |

555 |

556 | AppArmor is a kernel security module that confines programs to _____, reducing an application's attack surface 557 |

558 | a limited set of resources 559 |

560 | 561 |

562 |

563 | The _____ file contains encrypted passwords. 564 |

565 | /etc/shadow 566 |

567 | 568 |

569 |

570 | Linux passwords are encrypted with a random _____, allowing them to have several encrypted forms, especially if several users use the same password 571 |

572 | salt 573 |

574 | 575 |

576 |

577 | Linux typically encrypts passwords under the _____ cryptographic function 578 |

579 | SHA-512 580 |

581 | 582 |

583 |

584 | Each line in the _____ file represents a user. A line's colon-separated fields represent: username:password:UID:Default GID:comments:home:shell 585 |

586 | /etc/passwd 587 |

588 | 589 |

590 |

591 | Edit _____ by running vigr and /etc/gshadow by running vigr -s 592 |

593 | /etc/group 594 |

595 | 596 |

597 |

598 | The command groupadd _____ 599 |

600 | adds a user group 601 |

602 | 603 |

604 |

605 | The command vipw can change a user’s configuration through editing the _____ file 606 |

607 | /etc/passwd 608 |

609 | 610 |

611 |

612 | the chmod 0444 permission means READ permission for _____ 613 |

614 | owner, group and public 615 |

616 | 617 |

618 |

619 | Human groups should have GID of _____ 620 |

621 | 1000 or higher 622 |

623 | 624 |

625 |

626 | The commands useradd, usermod and userdel can be configured via the files /etc/login.defs and _____ 627 |

628 | /etc/default/useradd 629 |

630 | 631 |

632 |

633 | the chmod _____ permission means WRITE permission for owner, group and public 634 |

635 | 0222 636 |

637 | 638 |

639 |

640 | The command _____ changes a user's login shell 641 |

642 | chsh 643 |

644 | 645 |

646 |

647 | The command _____ lists users who are logged in. 648 |

649 | users 650 |

651 | 652 |

653 |

654 | A line in the /etc/group file represents a single group. Its fields are separated by colons: _____:Password:GID:Members, separated by commas 655 |

656 | Name 657 |

658 | 659 |

660 |

661 | Never manually edit /etc/passwd, /etc/group or /etc/shadow. Use the commands useradd, adduser, usermod, pw, vipw, _____ and chsh instead 662 |

663 | vipw -s 664 |

665 | 666 |

667 |

668 | The command groups displays _____ 669 |

670 | the groups a user belongs to 671 |

672 | 673 |

674 |

675 | A line in the /etc/group file represents a single group. Its fields are separated by colons: Name:Password:_____:Members, separated by commas 676 |

677 | GID 678 |

679 | 680 |

681 |

682 | Edit /etc/group by running vigr and /etc/gshadow by running _____ 683 |

684 | vigr -s 685 |

686 | 687 |

688 |

689 | A line in the _____ file represents a single group. Its fields are separated by colons: Name:Password:GID:Members, separated by commas 690 |

691 | /etc/group 692 |

693 | 694 |

695 |

696 | The _____ file configures password expiration, encryption algorithms, UID ranges and GID ranges 697 |

698 | login.defs 699 |

700 | 701 |

702 |

703 | The command pwconv reconciles the contents of the /etc/shadow and _____ files 704 |

705 | /etc/passwd 706 |

707 | 708 |

709 |

710 | Each line of the _____ password file represents a user. The user's fields are separated by colons: username:password:Last password change:Minimum days required between password changes:Maximum days between password changes:password expiration warning duration:password expiration ban deadline:{{c10::account expiration date}} 711 |

712 | /etc/shadow 713 |

714 | 715 |

716 |

717 | The command users _____ 718 |

719 | lists users who are logged in. 720 |

721 | 722 |

723 |

724 | _____ is a kernel security module that can sandbox syscalls in userspace via restricted seccomp filters 725 |

726 | gVisor 727 |

728 | 729 |

730 |

731 | The command _____ displays the currently logged in user 732 |

733 | whoami 734 |

735 | 736 |

737 |

738 | The commands useradd, usermod and userdel can be configured via the files _____ and /etc/default/useradd 739 |

740 | /etc/login.defs 741 |

742 | 743 |

744 |

745 | Each line of the /etc/shadow password file represents a user. The user's fields are separated by colons: username:password:Last password change:_____:Maximum days between password changes:password expiration warning duration:password expiration ban deadline:{{c10::account expiration date}} 746 |

747 | Minimum days required between password changes 748 |

749 | 750 |

751 |

752 | Each line in the /etc/passwd file represents a user. A line's colon-separated fields represent: username:password:UID:Default GID:_____:home:shell 753 |

754 | comments 755 |

756 | 757 |

758 |

759 | Users managed through LDAP (or other directory service) might have special entries in the /etc/passwd file beginning with _____, integrating the file with the directory service 760 |

761 | + or - 762 |

763 | 764 |

765 |

766 | The /etc/group file contains _____ 767 |

768 | group definitions. 769 |

770 | 771 |

772 |

773 | The _____ GID is used during creation of new files and directories 774 |

775 | default 776 |

777 | 778 |

779 |

780 | Edit /etc/group by running vigr and _____ by running vigr -s 781 |

782 | /etc/gshadow 783 |

784 | 785 |

786 |

787 | Grant a user sudo privileges by adding their username to the _____ file 788 |

789 | sudoers 790 |

791 | 792 |

793 |

794 | The _____ group always has GID of 0 795 |

796 | root, system, or wheel 797 |

798 | 799 |

800 |

801 | You can generate AppArmor profiles using the _____ generation tool 802 |

803 | Bane (https://github.com/jfrazelle/bane) 804 |

805 | 806 |

807 |

808 | Each line in the /etc/passwd file represents a user. A line's colon-separated fields represent: username:_____:UID:Default GID:comments:home:shell 809 |

810 | password 811 |

812 | 813 |

814 |

815 | gVisor is a kernel security module that can sandbox _____ in userspace via restricted seccomp filters 816 |

817 | syscalls 818 |

819 | 820 |

821 |

822 | seccomp filters decide which syscalls are allowed inside in a system. This prevents signals from being arbitrarily ran by an attacker, or being used to break out of a Linux namespace via _____ 823 |

824 | unshare 825 |

826 | 827 |

828 |

829 | A line in the /etc/group file represents a single group. Its fields are separated by colons: Name:_____:GID:Members, separated by commas 830 |

831 | Password 832 |

833 | 834 |

835 |

836 | The command _____ displays user and group ID's 837 |

838 | id 839 |

840 | 841 |

842 |

843 | The command chage -d 0 username _____ 844 |

845 | invalidates a user’s password and forces an update 846 |

847 | 848 |

849 |

850 | gVisor is a kernel security module that can sandbox syscalls in userspace via _____ 851 |

852 | restricted seccomp filters 853 |

854 | 855 |

856 |

857 | The _____ directory holds sample startup files 858 |

859 | /etc/skel 860 |

861 | 862 |

863 |

864 | The command _____ invalidates a user’s password and forces an update 865 |

866 | chage -d 0 username 867 |

868 | 869 |

870 |

871 | AppArmor is a _____ that confines programs to a limited set of resources, reducing an application's attack surface 872 |

873 | kernel security module 874 |

875 | 876 |

877 |

878 | It is best practice that a human user should have the same consistent login name and _____ across all machines they use 879 |

880 | UID 881 |

882 | 883 |

884 |

885 | The command groupmod_____ 886 |

887 | modifies a group 888 |

889 | 890 |

891 |

892 | The command groupdel _____ 893 |

894 | deletes a group 895 |

896 | 897 |

898 |

899 | The /etc/skel directory holds _____ 900 |

901 | sample startup files 902 |

903 | 904 |

905 |

906 | It is best practice that a human user should have the same consistent _____ and UID across all machines they use 907 |

908 | login name 909 |

910 | 911 |

912 |

913 | The _____ file defines groups 914 |

915 | /etc/group 916 |

917 | 918 |

919 |

920 | The command _____ creates a new user account. 921 |

922 | useradd 923 |

924 | 925 |

926 |

927 | LDAP and /etc/passwd integration can be configured in the _____ file 928 |

929 | /etc/nsswitch.conf 930 |

931 | 932 |

933 |

934 | The command _____ deletes a group 935 |

936 | groupdel 937 |

938 | 939 |

940 |

941 | RHEL's password encryption algorithm is set in the _____ file, or through the authconfig command 942 |

943 | /etc/login.defs 944 |

945 | 946 |

947 |

948 | gVisor is a kernel security module that can sandbox syscalls in _____ via restricted seccomp filters 949 |

950 | userspace 951 |

952 | 953 |

954 |

955 | Linux limits login length to _____ characters 956 |

957 | 32 958 |

959 | 960 |

961 |

962 | Never manually edit /etc/passwd, /etc/group or /etc/shadow. Use the commands useradd, adduser, _____, pw, vipw, vipw -s and chsh instead 963 |

964 | usermod 965 |

966 | 967 |

968 |

969 | The command pwconv reconciles the contents of the _____ and /etc/passwd files 970 |

971 | /etc/shadow 972 |

973 | 974 |

975 |

976 | To manually create a new Linux user, add them into the files: _____ 977 |

978 | /etc/passwd, /etc/shadow and /etc/group 979 |

980 | 981 |

982 |

983 | the chmod 0222 permission means WRITE permission for _____ 984 |

985 | owner, group and public 986 |

987 | 988 |

989 |

990 | Never manually edit /etc/passwd, /etc/group or /etc/shadow. Use the commands useradd, adduser, usermod, pw, vipw, vipw -s and _____ instead 991 |

992 | chsh 993 |

994 | 995 |

996 |

997 | Users managed through LDAP (or other directory service) might have special entries in the _____ file beginning with + or -, integrating the file with the directory service 998 |

999 | /etc/passwd 1000 |

1001 | 1002 |

1003 |

1004 | "The command grep login /var/log/* _____" 1005 |

1006 | searches the /var/log/ directory for usages of the word ""login"" 1007 |

1008 | 1009 | -------------------------------------------------------------------------------- /docs/shell.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | The command _____ displays a message on the screen 4 |

5 | echo 6 |

7 | 8 |

9 |

10 | The command _____ sleeps for a given time 11 |

12 | sleep 13 |

14 | 15 |

16 |

17 | The PATH _____ stores a list of directories that are searched for the binary of any command typed into a terminal 18 |

19 | environment variable 20 |

21 | 22 |

23 |

24 | The command _____ removes a variable or a function 25 |

26 | unset 27 |

28 | 29 |

30 |

31 | The command _____ can display lines which begin with a specified string 32 |

33 | look 34 |

35 | 36 |

37 |

38 | The command read _____ 39 |

40 | reads a line from stdin 41 |

42 | 43 |

44 |

45 | The PATH environment variable stores a list of directories that are searched for _____ of any command typed into a terminal 46 |

47 | the binary 48 |

49 | 50 |

51 |

52 | Enclosing a string between _____ characters makes it literal. 53 |

54 | single quote 55 |

56 | 57 |

58 |

59 | The command getopts _____ 60 |

61 | parses bash positional arguments 62 |

63 | 64 |

65 |

66 | The command _____ can fit text to a desired width 67 |

68 | fold 69 |

70 | 71 |

72 |

73 | The command bg _____ 74 |

75 | sends a process to the background 76 |

77 | 78 |

79 |

80 | The command _____ reads a line from stdin 81 |

82 | read 83 |

84 | 85 |

86 |

87 | The command _____ declares variables 88 |

89 | declare 90 |

91 | 92 |

93 |

94 | The command _____ re-runs the last command 95 |

96 | !! 97 |

98 | 99 |

100 |

101 | The command set _____ 102 |

103 | changes a config variable of the running shell 104 |

105 | 106 |

107 |

108 | "Enclosing a string between backtick `` characters makes it act as a command. Example: _____" 109 |

110 | echo ""Hello `whoami`"" 111 |

112 | 113 |

114 |

115 | The command _____ swaps the stdout and stderr of a command 116 |

117 | 3>&2 2>&1 1>&3 118 |

119 | 120 |

121 |

122 | The command unset _____ 123 |

124 | removes a variable or a function 125 |

126 | 127 |

128 |

129 | The PATH environment variable stores a _____ that are searched for the binary of any command typed into a terminal 130 |

131 | list of directories 132 |

133 | 134 |

135 |

136 | The command su _____ 137 |

138 | executes commands as another system user 139 |

140 | 141 |

142 |

143 | The command _____ parses bash positional arguments 144 |

145 | getopts 146 |

147 | 148 |

149 |

150 | The command echo _____ 151 |

152 | displays a message on the screen 153 |

154 | 155 |

156 |

157 | The command _____ executes commands as another system user 158 |

159 | su 160 |

161 | 162 |

163 |

164 | The command !! _____ 165 |

166 | re-runs the last command 167 |

168 | 169 |

170 |

171 | The command eval _____ 172 |

173 | evaluates commands and arguments passed to it 174 |

175 | 176 |

177 |

178 | The command sleep _____ 179 |

180 | sleeps for a given time 181 |

182 | 183 |

184 |

185 | The command _____ configures wireless network interfaces 186 |

187 | iwconfig 188 |

189 | 190 |

191 |

192 | The command _____ defines bash functions 193 |

194 | function 195 |

196 | 197 |

198 |

199 | The command _____ changes a config variable of the running shell 200 |

201 | set 202 |

203 | 204 |

205 |

206 | The command declare _____ 207 |

208 | declares variables 209 |

210 | 211 |

212 |

213 | The command fold _____ 214 |

215 | can fit text to a desired width 216 |

217 | 218 |

219 |

220 | The command _____ sorts text numerically 221 |

222 | sort -n 223 |

224 | 225 |

226 |

227 | The command _____ evaluates commands and arguments passed to it 228 |

229 | eval 230 |

231 | 232 |

233 |

234 | The command expr _____ 235 |

236 | evaluates expressions 237 |

238 | 239 |

240 |

241 | The command fmt _____ 242 |

243 | can be used to format text 244 |

245 | 246 |

247 |

248 | The command _____ evaluates expressions 249 |

250 | expr 251 |

252 | 253 |

254 |

255 | The command 3>&2 2>&1 1>&3 _____ 256 |

257 | swaps the stdout and stderr of a command 258 |

259 | 260 |

261 |

262 | The command iwconfig _____ 263 |

264 | configures wireless network interfaces 265 |

266 | 267 |

268 |

269 | The command _____ can be used to format text 270 |

271 | fmt 272 |

273 | 274 |

275 |

276 | The command look _____ 277 |

278 | can display lines which begin with a specified string 279 |

280 | 281 |

282 |

283 | The command sort -n _____ 284 |

285 | sorts text numerically 286 |

287 | 288 |

289 |

290 | The command function _____ 291 |

292 | defines bash functions 293 |

294 | 295 |

296 |

297 | The command local _____ 298 |

299 | creates a local variable 300 |

301 | 302 |

303 |

304 | The command _____ creates a local variable 305 |

306 | local 307 |

308 | 309 |

310 |

311 | The command _____ sends a process to the background 312 |

313 | bg 314 |

315 | 316 |

317 |

318 | The _____ environment variable stores a list of directories that are searched for the binary of any command typed into a terminal 319 |

320 | PATH 321 |

322 | 323 | -------------------------------------------------------------------------------- /docs/signals.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | Which signal can you send using the kill command? _____ 4 |

5 | Any signal! 6 |

7 | 8 |

9 |

10 | Signal 11 is _____ 11 |

12 | SIGSEGV (Segmentation fault) 13 |

14 | 15 |

16 |

17 | Signals 30 and 31 are _____ 18 |

19 | USR1 and USR2 (User-defined) 20 |

21 | 22 |

23 |

24 | Which signal can you send using the _____ command? Any signal! 25 |

26 | kill 27 |

28 | 29 |

30 |

31 | The signal _____ immediately destroys a process. It can't be blocked or caught by the process. Since it is done at kernel level, the process does not even actually receive this signal. 32 |

33 | SIGKILL 34 |

35 | 36 |

37 |

38 | Signal 15 is _____ 39 |

40 | SIGTERM (Software termination) 41 |

42 | 43 |

44 |

45 | Signal _____ is SIGTSTP (Keyboard stop) 46 |

47 | 18 48 |

49 | 50 |

51 |

52 | A process is running inside your user terminal. The _____ signal will be sent to it if you press Control+C on your keyboard. 53 |

54 | SIGINT 55 |

56 | 57 |

58 |

59 | Signal 1 is _____ 60 |

61 | SIGHUP (Hangup) 62 |

63 | 64 |

65 |

66 | Signal _____ is SIGKILL (Kill) 67 |

68 | 9 69 |

70 | 71 |

72 |

73 | Signal _____ is SIGSTOP (Stop) 74 |

75 | 17 76 |

77 | 78 |

79 |

80 | Signal 18 is _____ 81 |

82 | SIGTSTP (Keyboard stop) 83 |

84 | 85 |

86 |

87 | Signal 10 is _____ 88 |

89 | SIGBUS (Bus error) 90 |

91 | 92 |

93 |

94 | Can processes communicate via signals? _____ 95 |

96 | Yes 97 |

98 | 99 |

100 |

101 | The signal _____ is used as a reset request towards a process. 102 |

103 | SIGHUP 104 |

105 | 106 |

107 |

108 | Signal 3 is _____ 109 |

110 | SIGQUIT (Quit) 111 |

112 | 113 |

114 |

115 | A signal is received by a process. If it has one, the process executes a custom _____ for the specific singal. Otherwise, the kernel takes a ____ on its behalf. 116 |

117 | handler routine default action 118 |

119 | 120 |

121 |

122 | Signal _____ is SIGCONT (Continue after stop) 123 |

124 | 19 125 |

126 | 127 |

128 |

129 | A process's received signal and system calls it makes can be displayed with _____ 130 |

131 | strace 132 |

133 | 134 |

135 |

136 | When a handler routine is specified for a signal, the signal is referred to as being _____. 137 |

138 | caught 139 |

140 | 141 |

142 |

143 | The signals _____ and 17 (SIGSTOP) can't be caught, blocked or ignored by a receiving process. 144 |

145 | 9 (SIGKILL) 146 |

147 | 148 |

149 |

150 | Signal _____ is SIGHUP (Hangup) 151 |

152 | 1 153 |

154 | 155 |

156 |

157 | Process-level interrupt requests in Linux are called _____ 158 |

159 | Signals 160 |

161 | 162 |

163 |

164 | Can a process block a received SIGCONT signal? _____ 165 |

166 | No - it can be caught or ignored however 167 |

168 | 169 |

170 |

171 | Can signals be sent to communicate between processes? _____ 172 |

173 | Yes 174 |

175 | 176 |

177 |

178 | Signal _____ is SIGBUS (Bus error) 179 |

180 | 10 181 |

182 | 183 |

184 |

185 | The _____ records various information about each process, such as its priority, status, resource usage, opened ports and files, signal mask and address space map. 186 |

187 | kernel 188 |

189 | 190 |

191 |

192 | Signal _____ is SIGINT (Interrupt) 193 |

194 | 2 195 |

196 | 197 |

198 |

199 | The signals 9 (SIGKILL) and _____ can't be caught, blocked or ignored by a receiving process. 200 |

201 | 17 (SIGSTOP) 202 |

203 | 204 |

205 |

206 | You can suspend a process with the _____ signal, then resume it with the CONT signal. 207 |

208 | STOP 209 |

210 | 211 |

212 |

213 | You can suspend a process with the STOP signal, then resume it with the _____ signal. 214 |

215 | CONT 216 |

217 | 218 |

219 |

220 | Can the kernel send signals to a process to inform it of the death of its child process? _____ 221 |

222 | Yes 223 |

224 | 225 |

226 |

227 | Signal _____ is SIGQUIT (Quit) 228 |

229 | 3 230 |

231 | 232 |

233 |

234 | Signal _____ is SIGTERM (Software termination) 235 |

236 | 15 237 |

238 | 239 |

240 |

241 | Signal 17 is _____ 242 |

243 | SIGSTOP (Stop) 244 |

245 | 246 |

247 |

248 | Signal _____ is SIGSEGV (Segmentation fault) 249 |

250 | 11 251 |

252 | 253 |

254 |

255 | Signal 19 is _____ 256 |

257 | SIGCONT (Continue after stop) 258 |

259 | 260 |

261 |

262 | Signal _____ is SIGWINCH (Window changed) 263 |

264 | 28 265 |

266 | 267 |

268 |

269 | Signal 28 is _____ 270 |

271 | SIGWINCH (Window changed) 272 |

273 | 274 |

275 |

276 | Signal 9 is _____ 277 |

278 | SIGKILL (Kill) 279 |

280 | 281 |

282 |

283 | The kill command ran without any flags sends the _____ signal. 284 |

285 | SIGTERM 286 |

287 | 288 |

289 |

290 | The signals 9 (SIGKILL) and 17 (SIGSTOP) can't be caught, blocked or ignored by a receiving _____. 291 |

292 | process 293 |

294 | 295 |

296 |

297 | The _____ signal suspends the receiving process's execution until a SIGCONT signal is received. 298 |

299 | SIGSTOP 300 |

301 | 302 |

303 |

304 | Signals 10 and 11 (BUS and SEGV) suggest improper usage of _____ 305 |

306 | memory 307 |

308 | 309 |

310 |

311 | Signal 2 is _____ 312 |

313 | SIGINT (Interrupt) 314 |

315 | 316 | -------------------------------------------------------------------------------- /docs/syscalls.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | the syscalls for files are open(), close(), read() and _____ 4 |

5 | write() 6 |

7 | 8 |

9 |

10 | the _____ syscall adds a directory entry (hard link?) 11 |

12 | link 13 |

14 | 15 |

16 |

17 | the syscall _____ opens/creates a file and returns a file descriptor 18 |

19 | open 20 |

21 | 22 |

23 |

24 | The command _____ traces signals and system calls 25 |

26 | strace 27 |

28 | 29 |

30 |

31 | the syscalls for files are open(), close(), _____ and write() 32 |

33 | read() 34 |

35 | 36 |

37 |

38 | the syscalls for files are open(), _____, read() and write() 39 |

40 | close() 41 |

42 | 43 |

44 |

45 | A signal's _____ must perform a default action, invoke a handler function, block, or ignore it. 46 |

47 | receiving process 48 |

49 | 50 |

51 |

52 | The kernel code and function stubs used by each process are stored within _____ 53 |

54 | The address space pages of each process 55 |

56 | 57 |

58 |

59 | each process has 3 user IDs: _____ effective ID (determines privileges) saved ID (set by exec to match the effective ID) 60 |

61 | real ID (the owning user) 62 |

63 | 64 |

65 |

66 | the _____ syscall makes a symbolic link 67 |

68 | symlink 69 |

70 | 71 |

72 |

73 | the syscall _____ releases a file descriptor 74 |

75 | close 76 |

77 | 78 |

79 |

80 | each process has 3 user IDs: real ID (the owning user) effective ID (determines privileges) _____ 81 |

82 | saved ID (set by exec to match the effective ID) 83 |

84 | 85 |

86 |

87 | _____ gets/sets default permissions for new files/directories created henceforth by a process. 88 |

89 | umask 90 |

91 | 92 |

93 |

94 | Signals can either be sent by the kernel or _____ 95 |

96 | the kill syscall 97 |

98 | 99 |

100 |

101 | How many users can a file or directory be owned by at most? _____ 102 |

103 | One 104 |

105 | 106 |

107 |

108 | Can exec can change IDs of files via setuid? _____ 109 |

110 | Yes 111 |

112 | 113 |

114 |

115 | the file permission classes are _____, group, other 116 |

117 | user 118 |

119 | 120 |

121 |

122 | each file and directyory in a partition is known by a unique inode _____ 123 |

124 | number 125 |

126 | 127 |

128 |

129 | The command strace _____ 130 |

131 | traces signals and system calls 132 |

133 | 134 |

135 |

136 | the syscall _____ copies bytes from of memory to a file. Blocks 137 |

138 | write 139 |

140 | 141 |

142 |

143 | _____ expose functionalities of the operating system to programs. 144 |

145 | system calls 146 |

147 | 148 |

149 |

150 | "_____ performs ""memory mapping"" of pages to the process address space. munmap can then be used to unmap them." 151 |

152 | mmap 153 |

154 | 155 |

156 |

157 | A _____ represents one end of a connection as a channel of communication. 158 |

159 | socket 160 |

161 | 162 |

163 |

164 | "mmap performs ""memory mapping"" of pages to the process address space. _____ can then be used to unmap them." 165 |

166 | munmap 167 |

168 | 169 |

170 |

171 | the file permission classes are user, _____, other 172 |

173 | group 174 |

175 | 176 |

177 |

178 | the _____ for files are open(), close(), read() and write() 179 |

180 | syscalls 181 |

182 | 183 |

184 |

185 | _____ changes permissions of an existing file/directory. The invoking process' EUID must be 0, or match the owner of that file/directory. 186 |

187 | chmod 188 |

189 | 190 |

191 |

192 | Signals can either be sent by _____ or the kill syscall 193 |

194 | the kernel 195 |

196 | 197 |

198 |

199 | a partition's root directory always has inode number _____ 200 |

201 | 2 202 |

203 | 204 |

205 |

206 | the syscall _____ copies bytes from a file to memory. Blocks. 207 |

208 | read 209 |

210 | 211 |

212 |

213 | each process has 3 user IDs: real ID (the owning user) _____ saved ID (set by exec to match the effective ID) 214 |

215 | effective ID (determines privileges) 216 |

217 | 218 |

219 |

220 | _____ changes the owner of an existing file/directory. The EUID of the invoker must be 0 or the owner of the file/directory. 221 |

222 | chown 223 |

224 | 225 |

226 |

227 | A file is ready to be released/overwritten once its _____'s link count equals 0. 228 |

229 | inode 230 |

231 | 232 |

233 |

234 | the syscalls for files are _____, close(), read() and write() 235 |

236 | open() 237 |

238 | 239 |

240 |

241 | Are syscalls ran inside the kernel? _____ 242 |

243 | No - they're only ever called from inside a process. Every process has its own copy of available syscall definitions inside its address space. This avoids making a CPU-expensive context switch to the kernel. 244 |

245 | 246 |

247 |

248 | the file permission classes are user, group, _____ 249 |

250 | other 251 |

252 | 253 | -------------------------------------------------------------------------------- /docs/system.md: -------------------------------------------------------------------------------- 1 |

2 |

3 | The _____ directory contains startup scripts and services. 4 |

5 | /etc/init.d 6 |

7 | 8 |

9 |

10 | The command _____ prints the systemd journal logs for a specific service unit 11 |

12 | journalctl -u [UNIT] 13 |

14 | 15 |

16 |

17 | The command _____ sets an environment variable 18 |

19 | export 20 |

21 | 22 |

23 |

24 | The directory /boot predominantly stores _____ 25 |

26 | boot loader static files 27 |

28 | 29 |

30 |

31 | _____ allows Linux not to have to rescrape its own filesystem if it goes down. 32 |

33 | Journalling 34 |

35 | 36 |

37 |

38 | The command _____ prints kernel ring file and driver messages 39 |

40 | dmesg 41 |

42 | 43 |

44 |

45 | The command export _____ 46 |

47 | sets an environment variable 48 |

49 | 50 |

51 |

52 | The command _____ prints the current user's environment variables 53 |

54 | env 55 |

56 | 57 |

58 |

59 | The _____ and /etc/grub.conf files contain init process configuration. 60 |

61 | /etc/inittab 62 |

63 | 64 |

65 |

66 | The command env _____ 67 |

68 | prints the current user's environment variables 69 |

70 | 71 |

72 |

73 | The directory /var predominantly stores _____ 74 |

75 | log files, spool files, variable size files 76 |

77 | 78 |

79 |

80 | The command dmesg _____ 81 |

82 | prints kernel ring file and driver messages 83 |

84 | 85 |

86 |

87 | _____ allows Linux to replay its work thus far and complete all incomplete transactions in case of outage. 88 |

89 | Journaling 90 |

91 | 92 |

93 |

94 | The command _____ displays information about the operating system 95 |

96 | uname 97 |

98 | 99 |

100 |

101 | The /etc/inittab and _____ files contain init process configuration. 102 |

103 | /etc/grub.conf 104 |

105 | 106 |

107 |

108 | The command journalctl -u [UNIT] _____ 109 |

110 | prints the systemd journal logs for a specific service unit 111 |

112 | 113 |

114 |

115 | The command uname _____ 116 |

117 | displays information about the operating system 118 |

119 | 120 |

121 |

122 | The directory /srv predominantly stores _____ 123 |

124 | Files saved by running servers and services (like Apache) 125 |

126 | 127 | -------------------------------------------------------------------------------- /mkdocs.yml: -------------------------------------------------------------------------------- 1 | site_name: Linux FAQ 2 | site_url: https://katademy.github.io/linux-faq 3 | site_author: Icelyn Jennings 4 | site_description: Learn Linux, flashcards, certification, interview questions. 5 | 6 | repo_url: https://github.com/katademy/linux-faq/ 7 | repo_name: linux-faq 8 | 9 | theme: 10 | favicon: favicon.png 11 | icon: 12 | logo: material/cloud 13 | custom_dir: overrides 14 | features: 15 | - header.autohide 16 | name: material 17 | palette: 18 | - scheme: default 19 | toggle: 20 | icon: material/toggle-switch-off-outline 21 | name: Switch to dark mode 22 | - scheme: slate 23 | toggle: 24 | icon: material/toggle-switch 25 | name: Switch to light mode 26 | 27 | extra: 28 | social: 29 | - icon: fontawesome/brands/twitter 30 | link: https://twitter.com/katademy 31 | name: katademy on Twitter 32 | - icon: fontawesome/brands/github 33 | link: https://github.com/katademy 34 | name: katademy on GitHub 35 | - icon: fontawesome/brands/linkedin 36 | link: https://www.linkedin.com/company/katademy 37 | name: katademy on LinkedIn 38 | - icon: fontawesome/brands/patreon 39 | link: https://patreon.com/icelynjennings 40 | name: icelynjennings on Patreon 41 | - icon: fontawesome/brands/paypal 42 | link: https://www.paypal.me/icelynjennings 43 | name: icelynjennings on PayPal 44 | 45 | copyright: "© 2020-2021 Icelyn Jennings" 46 | -------------------------------------------------------------------------------- /overrides/main.html: -------------------------------------------------------------------------------- 1 | {% extends "base.html" %} 2 | 3 | {% block announce %} 4 | For updates follow @katademy 5 | {% endblock %} 6 | --------------------------------------------------------------------------------