└── README.md /README.md: -------------------------------------------------------------------------------- 1 | # Linux commands 2 | 3 | ## Help 4 | |Command|Example|Comment| 5 | |--------|---|---| 6 | |man ``|man cd
man ls|**Manual**
Get help (close with q).| 7 | |`` --help|cd --help|Also **help**.| 8 | |Tab (1x or 2x) | |Auto completion.| 9 | |↑| |See previous command.| 10 | |Ctrl+C| |Kill the current process or command (e.g. if something hangs).| 11 | |Ctrl+D| |Logout. Closes the console if you're not in an ssh session. Similar to `exit`. | 12 | |Ctrl+R| |Search through your history. Start typing and it will auto-complete. Hit Ctrl+R again and it will cycle though the other auto-completion options. Hit Enter and the command will execute. Hit ←,→ to edit commands.| 13 | 14 | Have a look at this as well: [Modern Unix Alternatives](https://github.com/ibraheemdev/modern-unix) 15 | 16 | ## Basics 17 | |Command|Example|Comment| 18 | |---|---|---| 19 | |sudo ``| sudo ls
sudo !! | **Super user do**
Run a command with elevated privleges. Will ask you for a password. Only possible, if you were granted administrative rights on the system. sudo !! executes the last command with elevated privleges. 20 | |cd ``|cd test
cd ..
cd -
cd ~
cd /path/to/my/folder | **Change directory**
. (dot) is the current directory
.. (dotdot) is the upper/partent directory
/ (slash) is the root directory
~ (tilde) is your home directory
- (minus) switches to the previous directory| 21 | |ls
ls ``
ls ``
ls `` | ls
ls -la
ls -l -a (same as above)
ls -halt (more arguments)
ls -d \*/ (list all directories)
ls test (contents of subfolder)
ls \*.txt (show only .txt files) | **List** contents of a folder
-h human readable
-a all
-l more information
-t order by time | 22 | |mkdir ``
mkdir -p `` |mkdir test| **Make directory**
Creates a new immediate subfolder with the given name.
-p Create path. | 23 | |pwd | | **Print working directory**
Shows the current path.| 24 | |mv `` `` | mv text.txt test
mv test.txt bla.txt |**Move** a file
Can also be used for renaming (second example).
[progress](https://github.com/Xfennec/progress)| 25 | |cp `` ``| cp text.txt test
cp -p text.txt test | **Copy** a file
-p preserves mode, ownership, and timestamps
Can also rename.
[progress](https://github.com/Xfennec/progress)| 26 | |rm ``
rm -rf ``|rm text.txt
rm -rf test
rm \*.tmp (removes all files with file ending \*.tmp)| **Remove**
*Warning: Cannot be undone!*
-f force, no confirmation dialog
-r recursive, for folders | 27 | |clear| | **Clear** the console.
Gives you a fresh view. Similar to Ctrl+L| 28 | |reset| | **Reset** the console.
Like clear but more powerful. | 29 | 30 | ## More Basics 31 | |Command|Example|Comment| 32 | |---|---|---| 33 | |head ``
tail `` | head text.txt
head -n 20 text.txt | **Display first/last lines of file**
Default n=10.| 34 | |less `` | less text.txt | **Display contents of a file**
of a file, read-only
h help
q close
f,b forward, backward one page
e,y forward, backward single line
/`` search
n,p next, previous `` during search
-i activate case insentitive search | 35 | |nano `` | nano text.txt | **File editor**
Ctrl+x to close
Alt+/ to go to the end of a file | 36 | |chmod `` ``
chmod -R `` ``|chmod 777 file.txt
chmod -R 777 my_folder|**Change permissions**
-R recursive
777 gives the folder all possible rights.
Further explanation see below. | 37 | |chown `` `` | sudo chown alice folder | **Change file owner** | 38 | |du `` | du -h
du -sh .
du -sh * | sort -h | **Disk usage**
-s summary
-h human readable | 39 | |df `` | df -h | **Disk free**
Show remaining disk space.
-h human readable | 40 | |htop| | **Task manager**
View currently running processes. Q to close.| 41 | |sudo shutdown now
sudo reboot now| | **Shutdown / Reboot** | 42 | 43 | ## Multiple Commands 44 | |Command|Example|Comment| 45 | |---|---|---| 46 | | `` ; `` | | **Concatenate commands**
Execute `` after ``. | 47 | | `` && `` | | **Double ampersand**
Execute `` after `` but only if `` finished successfully. | 48 | | `` > ``
`` >> ``
`` 2> ``
`` &> `` | ls -a > result.txt
ls -a >> result.txt | **Redirect**
the output of a command into a file
> creates/overwrites a file
>> creates/appends to a file
2> redirects the errors
&> redirects both standard output and standard error | 49 | | `` | `` | history | less
ls | less | **Pipe**
the output of a command to less.
Especially useful for history command (displays the latest commands) or folders with many files in them (last example) | 50 | 51 | ## Misc 52 | |Command|Example|Comment| 53 | |---|---|---| 54 | |passwd `` | passwd alice | **Change password** | 55 | |rsync `` `` | rsync -aP file.txt servername:/home/user/data | **Rsync**
copy files from/to a server | 56 | |scp `` `` | `scp username@example.com:/my/folder/*.txt .` | **Secure copy**
files from/to a server
-r recursive (include subfolders)
The example copies all files from the given directory then end in .txt to the local directory (dot) | 57 | |ssh ``
ssh -t `` "``" | ssh `username@example.com`
ssh -t `username@example.com` "ls -a" | **Secure shell**
Connect to a server
-t Close connection immediately after the command is done
Further explanation see below. | 58 | |stat `` | stat text.txt | Display file **Status**, creation date,
last modification date, etc. | 59 | |su ``| su root | **Switch user** | 60 | |touch `` | touch text.txt
touch makefile | **Touch** a file.
Creates a new, empty file if the file does
not already exist.
Especially helpful to create makefiles under Windows.
Actually the command is used for changing file timestamps. | 61 | |watch| watch -n60 ls | Repeat a command every n seconds. | 62 | |which| which nano | Display where the command / program is coming from. | 63 | 64 | ## Cursor Tricks 65 | |Command|Comment| 66 | |---|---| 67 | |Ctrl+A|Jump to beginning.| 68 | |Ctrl+E|Jump to end.| 69 | |Ctrl+W|Delete one word left of the cursor.| 70 | |Ctrl+U|Delete entire line.| 71 | |Ctrl+Y|Paste back what you just deleted.| 72 | 73 | ### Grep 74 | ```bash 75 | grep 76 | # Search Within Files using Regular Expressions 77 | # Syntax: grep

78 | # 79 | # -i ignore case 80 | # -n show line numbers 81 | # -R recursive 82 | # -I ignore binary files 83 | # -l print out file names instead 84 | # -P Perl syntax \d \w \s 85 | # -E extended syntax [[:digit:]] [[:alpha:]] [[:space:]] 86 | # {2} exactly, {1,3} from to, {2,} two or more 87 | # --include=*.py search only in .py files. 88 | 89 | # Search word needle in file haystack.txt 90 | grep 'needle' haystack.txt 91 | 92 | # Search in .py files of current and all subdirectories, ignore case, print filenames only 93 | grep -Rli --include=*.py 'needle' * 94 | ``` 95 | More: [Intro](https://github.com/zeeshanu/learn-regex), [Ex1](http://www.robelle.com/smugbook/regexpr.html), [Ex2](http://marvin.cs.uidaho.edu/Teaching/CS445/regex.html), [RegExr](https://regexr.com/). 96 | 97 | ### Find 98 | ```bash 99 | find 100 | # Find Files or Directories Based On Name 101 | # Syntax: find 102 | # 103 | # -type f=search only files, d=search only directories 104 | # -name name 105 | # -iname caseinsensitive name 106 | 107 | # List all file names and directory names containing needle 108 | find . -name 'needle' 109 | 110 | # List only file names containing needle 111 | find . -type f -name 'needle' 112 | 113 | # List all files ending in .py 114 | find . -type f -name "*.py" 115 | 116 | # List all files ending in .py, containing needle, hide error messages 117 | find . -type f -name "*.py" -exec grep -li 'needle' {} + 118 | 119 | # Recursively count number of files in all subdirectories 120 | find . -type f | wc -l 121 | 122 | # Unzip files 123 | find . -name '*.zip' -print0 | xargs -0 -I {} -P 10 unzip -qq {} 124 | 125 | # Unzip files without going into subdirectories 126 | find . -maxdepth 1 -name '*.zip' -print0 | xargs -0 -I {} -P 10 unzip -qq {} 127 | ``` 128 | More: [Ex1](http://www.binarytides.com/linux-find-command-examples/), [Ex2](https://en.wikibooks.org/wiki/Guide_to_Unix/Commands/Finding_Files). 129 | 130 | ## Screen 131 | |Command|Comment| 132 | |---|---| 133 | |screen | Create a new session. | 134 | |Ctrl+A,D | Detach from current screen session. | 135 | |Ctrl+D | End current session. Similar to `exit`. | 136 | |screen -r | Reattach to session. | 137 | |screen -ls | List all sessions. | 138 | |screen -S `` -L | Create a new screen session `` with logging enabled. | 139 | |screen -r ``| Reattach to session with `` if there are multiple ones. | 140 | |screen -rx ``| Attach to session that is already attached. | 141 | |Ctrl+A,Esc | Enter scroll mode. Use ↑ and ↓ or Pg Up and Pg Dn to scroll. Hit Esc to exit scroll mode. | 142 | 143 | ## Creating an SSH key 144 | 145 | ```bash 146 | # Creating 147 | ssh-keygen -t rsa -b 4096 -N "" -C "" -f keyname 148 | mv keyname* ~/.ssh 149 | 150 | # Setting access rights 151 | chmod 700 ~/.ssh && chmod 600 ~/.ssh/* 152 | 153 | # ~/.ssh/config 154 | Host github 155 | HostName github.com 156 | User git 157 | IdentityFile ~/.ssh/keyname 158 | 159 | # This logs into the server, and copies the public key to it. 160 | ssh-copy-id -i ~/.ssh/keyname user@remote_machine 161 | ``` 162 | 163 | ```bash 164 | # Checking the ssh procesd 165 | ssh -T git@github.com 166 | eval $(ssh-agent -s) 167 | ssh-add ~/.ssh/keyname 168 | ssh -T git@github.com 169 | ``` 170 | 171 | ## Permissions 172 | 173 | Type `chmod xxx ` to change permissions where `xxx` is the numerical code from the table below. 174 | 175 | ``` 176 | Explaination of the Codes: . ... ... ... 177 | (type) (user persmissions) (group permissions) (world permissions) 178 | ``` 179 | The first item can be `d` (a directory), `-` (a regular file) or `l` (a symbolic link). 180 | The following three triplets specify permissons for the `user`, `group` and `world` in that order. 181 | In each tripplet, permissions can be `r` (read), `w` (write), `x` (execute) or `-` (not assigned). 182 | Setting permissions can be done via numbers: `r=4`, `w=2`, `x=1` and `-=0`. 183 | 184 | |Setting|Code|Use Case| 185 | |---|---|---| 186 | |`----------`|000|Locking even yourself out. Use `chmod` again, if this happens. | 187 | |`-r--------`|400|An auto-generated password file (e.g. `~/.google_authenticator`). | 188 | |`-rw-------`|600|`~/.history`, all the ssh keys in your `~/.ssh` folder.| 189 | |`-rwx------`|700|Your `~/.ssh` folder.| 190 | |`-r--r--r--`|444|A textfile, that others should see as well, but nobody should modify it.| 191 | |`-r-xr-xr-x`|555|A folder, that others should be able to `cd` into as well, but nobody should modify it.| 192 | |`-rwxr-xr-x`|755|Files and folders you want other people to *see*. | 193 | |`-rwxrwxrwx`|777|Files and folders you want other people to *see and modify*. The most open permission.| 194 | 195 | Permissions on directory have the following meaning: 196 | The read bit allows to list the files within the directory. 197 | The write bit allows to create, rename, or delete files within the directory, and modify the directory's attributes. 198 | The execute bit allows to enter the directory, and access files and directories inside. 199 | 200 | To view permissions as numerical code: `stat -c %a `. 201 | 202 |

What does `s` mean? (click to expand)

203 | "s", like "x", means something different for directories and regular files. 204 | 205 | For files, "x" means "executable" of course. For directories, it means "searchable." Without "x" permission on a directory, you can't set it to be your current directory, or get any of the file information like size, permissions, or inode number, so that you effectively can't access any of the files. If a directory has no "r" permission, you can't get a listing, but if you know a file is there, you can still access the file. 206 | 207 | Now "s", for files, means "setuid exec." If a file has s permission, then it's executable, and furthermore, the user id and/or group id of the process is set to the user or group id of the owner of the file, depending on whether it's the user or group "s" that's set. This is a way to give limited root powers to a user -- a program that runs as root when an ordinary user executes it. For example, the "passwd" program, which can change otherwise write-protected files on behalf of a user, works this way: it's owned by the "bin" group (generally) and has g+s so that it can write to /etc/passwd and/or /etc/opasswd which are also owned by group "bin." 208 | 209 | For directories, "s" means "sticky". If a directory has "s", then the owner and/or group of any files put into the directory are set to the owner/group of the directory. This is often used on CVS repositories, so that the files in the repository end up all owned by the same person and/or group, even though they're put in by different people. I use g+s on all the CVS repositories I set up. 210 |

211 | 212 | 213 | ## Snippets and Useful .bashrc Additions 214 | 215 | ```bash 216 | # Finding out which linux you are using 217 | uname -m && cat /etc/*release 218 | 219 | # Bulk renaming of files 220 | rename 's/ch0/ch/gi' *.tiff 221 | ``` 222 | 223 | ```bash 224 | # Make output of df and du human readable 225 | alias df='df -h' 226 | alias du='du -h' 227 | 228 | # Count files in directory 229 | alias fcount='ls -1 | wc -l' 230 | 231 | # Disable "Save workspace" promt when closing R 232 | alias R='R --no-save' 233 | ``` 234 | 235 | ## Resources 236 | * [fselect](https://github.com/jhspetersson/fselect) - Search for files in a modern, SQL-like fashion. 237 | * [Modern Unix Alternatives](https://github.com/ibraheemdev/modern-unix) 238 | * [Presentation](https://ketancmaheshwari.github.io/pdfs/LPT_LISA.pdf) 239 | * [Linux Directories Explained in 100 Seconds](https://www.youtube.com/watch?v=42iQKuQodW4) 240 | --------------------------------------------------------------------------------