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Fred B.
Fred B.

Posted on • Updated on

Ubuntu/Linux cmd-line Cheat Sheet

#bash #ubuntu #linux
Originally posted on Codepen Oct 30, 2015

Convert binary, hex, or any base, into decimal

from hex to decimal: $((16#62)) => 98 (note the 16#)
from binary to decimal: $((2#01110011)) => 115 (note the 2#)
Note: the expression $(()) will execute a command named according to what it returns, so echo it to avoid the prompt complaining that it knows no command named 98 or 115

picoplayer@challenge:~$ $((16#62))
98: command not found
picoplayer@challenge:~$ echo $((16#62))
98
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Convert ASCII hex value into the actual characters

note: also works with 0x prefix, ie: 0x62 0x64 0x61 0x36 0x38 0x66 0x37 0x35

$ echo "62 64 61 36 38 66 37 35" | xxd -p -r
bda68f75
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Convert to text from [binary|octal|hex] 

$ x="01100011 01101111 01101101 01110000 01110101 01110100 01100101 01110010"
$ for a in $x; do printf "%x" $((2#$a)); done | xxd -r -p && echo " "
computer
$ x="160 145 141 162"
$ for a in $x; do printf "%x" $((8#$a)); done | xxd -r -p && echo " "
pear
$ x="66616c636f6e"
$ for a in $x; do printf "%x" $((16#$a)); done | xxd -r -p && echo " "
falcon
$
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Convert character into decimal ASCII value 

$ printf "%d\n" "'a"
97
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Convert decimal ASCII value into a character 

$ printf "%x" 97 | xxd -r -p
a
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Convert decimal ASCII value into hex value 

$ printf "%x" 97
61
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List sudo available commands: sudo -l

Bypassing permissions

As can be seen in the output below, the challenge directory is not accessible since no permissions have been set (0 d--------- 1 root root 27 Aug 4 21:34 challenge).

picoplayer@challenge:~$ cd /
picoplayer@challenge:/$ ls -ls

total 0
0 lrwxrwxrwx    1 root   root      7 Mar  8  2023 bin -> usr/bin
0 drwxr-xr-x    2 root   root      6 Apr 15  2020 boot
0 d---------    1 root   root     27 Aug  4 21:34 challenge
0 drwxr-xr-x    5 root   root    340 Dec 13 17:55 dev
0 drwxr-xr-x    1 root   root     66 Dec 13 17:55 etc
0 drwxr-xr-x    1 root   root     24 Aug  4 21:32 home
0 lrwxrwxrwx    1 root   root      7 Mar  8  2023 lib -> usr/lib
0 lrwxrwxrwx    1 root   root      9 Mar  8  2023 lib32 -> usr/lib32
0 lrwxrwxrwx    1 root   root      9 Mar  8  2023 lib64 -> usr/lib64
0 lrwxrwxrwx    1 root   root     10 Mar  8  2023 libx32 -> usr/libx32
0 drwxr-xr-x    2 root   root      6 Mar  8  2023 media
0 drwxr-xr-x    2 root   root      6 Mar  8  2023 mnt
0 drwxr-xr-x    2 root   root      6 Mar  8  2023 opt
0 dr-xr-xr-x 2501 nobody nogroup   0 Dec 13 17:55 proc
0 drwx------    1 root   root     23 Aug  4 21:34 root
0 drwxr-xr-x    1 root   root     54 Dec 13 17:56 run
0 lrwxrwxrwx    1 root   root      8 Mar  8  2023 sbin -> usr/sbin
0 drwxr-xr-x    2 root   root      6 Mar  8  2023 srv
0 dr-xr-xr-x   13 nobody nogroup   0 Dec 13 17:55 sys
0 drwxrwxrwt    1 root   root      6 Aug  4 21:34 tmp
0 drwxr-xr-x    1 root   root     18 Mar  8  2023 usr
0 drwxr-xr-x    1 root   root     17 Mar  8  2023 var
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So the idea, is to use vi to access the contents of the challenge directory anyway, because as seen in the last line of the following output, vi can be used with sudo

picoplayer@challenge:/$ sudo -l
Matching Defaults entries for picoplayer on challenge:
    env_reset, mail_badpass,
    secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User picoplayer may run the following commands on challenge:
    (ALL) /usr/bin/vi
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So, finally:

  1. type sudo vi,
  2. type :! ls -ls /challenge/
  3. read the following output 
picoplayer@challenge:/$ sudo vi
[sudo] password for picoplayer: 

4 ---------- 1 root root 98 Aug  4 21:34 metadata.json
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I now even can print the contents of that file. So, still from vi, type :! cat /challenge/metadata.json

Convert string to MD5 hash 

# to avoid the trailing newline added by the shell: '%s'
printf '%s' "money" | md5sum
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Determining the contents of non-text files, like a binary file for example. 

strings -a -t x [path-to-binary-file-for-example]
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Create a binary (executable) file from a bash script (install shc) 

# This will create 2 files, and the binary/exec one is 'add.sh.x'
shc -f add.sh
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View contents of binary file 

# bvi, bview - visual editor for binary files
bvi ./add.sh.x
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Is package installed? 

dpkg -s gimp
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Update all packages at once

Disclaimer: this command should probably never be used in an actual production server ;)

sudo apt-get install -f
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Free port 

kill $(lsof -t -i:3000)
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LAN Access for WSL localhost

These are Powershell (run as admin) commands. (source1 | source2)

netsh advfirewall firewall add rule name="Allowing connections to WSL2 servers" dir=in action=allow protocol=TCP localport=3000

netsh interface portproxy add v4tov4 listenport=3000 listenaddress=0.0.0.0 connectport=3000 connectaddress=[plug here the result of `wsl hostname -I`]
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To show added rule & proxy 
netsh advfirewall firewall show rule name="Allowing connections to WSL2 servers"

netsh interface portproxy show v4tov4
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Install a package (.deb) 

sudo dpkg -i /path/to/deb/file
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create a tree of directories in one command 

mkdir -pv dir1/dir2/dir3/dir4/dir5
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The above commands will create directory(s) recursively inside a non-existent directory(s). You can use the 'tree' command to view the directory structure.

tree dir1/
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dir1/
└── dir2
 └── dir3
 └── dir4
 └── dir5
4 directories, 0 files
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Find files recursively in all subdirectories and list them by DESC file size 

ls -lhR | grep -E "\.(jpg|zip)$" | awk '{print $5, $9}' | sort -hr
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Or,

find . -type f -exec du -h {} + | grep -E "\./.*\.(jpg|zip)" | sort -hr
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Find files by name in a directory tree

This search is case insensitive (-ipath) and recursively traverses the all subdirectories.
The path

find -ipath */ubeR-secret.txt
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Output:

./adequate_books/more_books/.secret/deeper_secrets/deepest_secrets/uber-secret.txt
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Using command output as the parameter of another command

Just place it between $([command]).
I should call that this works because I'm expecting a single result in the output. Unexpected results might happen if cat (or the encapsulating command) was fed a multiline result as parameters...

cat $(find -ipath */ubeR-secret.txt)
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List files that were created between 2 dates 

find . -type f -newermt "2012-01-01" \! -newermt "2020-09-01"
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Search for file contents in a directory tree recursively 

grep -r "pico"
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Output:

big-zip-files/folder_pmbymkjcya/folder_cawigcwvgv/folder_ltdayfmktr/folder_fnpfclfyee/whzxrpivpqld.txt:information on the record will last a billion years. Genes and brains and books encode picoCTF{gr3p_15_m4g1c_ef8790dc}

make script file executable 

chmod +x [filename]
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Get local IP address 

hostname -I | awk '{print $1}'
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Open current terminal location into file explorer 

xdg-open file
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Download file to current directory, using the name and extension found in the URL 

wget https://raw.githubusercontent.com/ariya/phantomjs/master/examples/printenv.js
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Create a symbolic link 

ln -s /path/to/original /path/to/symlink
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Saving as unix file from VIM 

:set fileformat=unix
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Find what PID is locking a port 

netstat -tulpn | grep <port>
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Force kill a PID 

kill -9 <PID>
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Find out what process is locking a file 

fuser <file_path>
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Avoid being prompted for private key when using SSH or scp to connect to hosts with your public key. 

 eval `ssh-agent`
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 ssh-add
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Command to kill a UI/Desktop Application 

xkill
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Terminator preferences profile (~/.config/terminator/config) 

[global_config]
[keybindings]
[profiles]
  [[default]]
    use_system_font = False
    background_image = None
    background_darkness = 0.91
    active_encodings = ANSI_X3.4-1968, UTF-8, ISO-8859-1
    foreground_color = "#839496"
    font = Ubuntu Mono 14
    background_color = "#002b36"
    scrollback_infinite = True
[layouts]
  [[default]]
    [[[child1]]]
      type = Terminal
      parent = window0
    [[[window0]]]
      type = Window
      parent = ""
[plugins]
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My custom bash prompt 

########### current_dir(current_git_branch) ####################
parse_git_branch() {
 git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/(\1)/'
}

RED="\[\033[0;31m\]"
YELLOW="\[\033[0;33m\]"
GREEN="\[\033[0;32m\]"
NO_COLOR="\[\033[0m\]"

PS1="$GREEN\W$YELLOW\$(parse_git_branch)$NO_COLOR "
####################
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Cancel reverse-i-search 

Ctrl+G
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Activate reverse-i-search 

Ctrl+R
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Reload bash prompt after .bashrc modification 

source .bashrc
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Google chrome path 

which google-chrome
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Check ubuntu version 

lsb_release -a
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Make umount Work with sshfs 

fusermount -u /path/to/mounted-dir
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Get a report of the used and available space on all mounted drives 

df -h
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Get a report of the size of data by folder 

sudo du -sk /home/* > tmp3.txt
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Sort report 

sort -n tmp.txt
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Get a list of processes, ssh in this case 

ps -ax | grep ssh
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Print number of .tpl files (from current directory and in all nested directories..) 

find -name '*.tpl' | wc -l
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Print a list of .tpl files (from current directory and in all nested directories..) 

find -name '*.tpl'
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Look for the number of files (.tpl in this case) per directory 

 for D in *; do echo $D; find $D -type f -name '*.tpl'| wc -l; done
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