Linux cheatsheet

Basic

• cd [directory] : change directory
  • cd !$ : change directory to last arg
• ls [directory] : list files & directories
  • -l : list
  • -a : all (hidden too)
  • -h : human sizes
• cp [src] [dst] : copy src to dst
  • -r : recursive (directory)
• rm [file or directory] : remove file or directory
  • -r : recursive (directory)
  • -f : force
• mkdir [directory] : create directory
  • -p : create parent directories as needed
• ln -s [target] [symlink] : create a symlink
• ln [target] [hardlink] : create a hardlink (same inode)
• touch [file] : create empty file, mark file as newly edited
• source [file] : execute a .sh file within the current shell
• cat [file] : print file to the screen
• tree -a : print directory hierarchy
  • -a : show all files (hidden)
  • -L [max depth] : max depth
• tail -n [num of lines] [file] : show last N lines of a file
• file [file] : get file type
• stat [file] : get file info (modified, access, creation time)
• man [cmd] : show manual for cmd
• tldr [cmd] : show short help for cmd
• pwd : show current directory
• which [cmd] : show where cmd is located
• history : show bash history
• find : find files
  • find [directory] -name [file] : find file in directory
  • find [directory] -name *.[ext] : find all files of a given type
  • find [directory] -type f -exec grep "[text]" '{}' \; -print : find text in files
  • find / -name "[pattern]" 2>/dev/null : find all and ignore errors

Other

• reboot : reboot system
• poweroff : shutdown system
• wget : ?
• curl [url] : get web page
  • -I : only get HTTP headers not body
  • -v : verbose
• tar -czvf [output file] [input dir] : create tar file (tar.gz)
• tar -xvf [input file] -C [output dir] : extract tar file
• zip : ?
• unzip : ?
• hexdump : dump file as hexa
• find . -name [file] | entr [cmd] : run a cmd whenever a file changes
• time [cmd] : time execution of cmd

Permissions

• sudo [cmd] : run a cmd as root
• chmod u=,g=,o= [file] : change file permissions
  • -R : recursive
  • +x : make a file executable
  • +rw : make a file read-write
  • -w : make a file read-only
  • +rx : make directory traversable
• chmod [number] [file] : change file permissions
• ls -la : list file permissions

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owner(u) group(g) other(o)
d rwx rwx rwx owner group

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number is made of 3 digits (octal, base 8):
U G O

4 = r
2 = w
1 = x

7 = rwx
6 = rw
5 = rx
4 = r
3 = wx
2 = w
1 = x
0 = 

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Default file permissions
fedora (most common)
    Files:       644 = rw- r-- r--
    Directories: 755 = rwx r-x r-x
debian
    Files:       664 = rw- rw- r--
    Directories: 775 = rwx rwx r-x

• cat /etc/passwd : list all users
• chown [owner] [file] : change owner of a file
• chgrp [group] [file] : change group of a file
• chown [owner]:[group] [file] : change the owner + group of a file
  • -R : recursive
• usermod -aG [group] [user] : add user to group
• sudo gpasswd -d [user] [group] : remove user from a group
• newgrp [group] : create group
• groups [user] : list groups of a user
• cat /etc/group : list all groups

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docker:x:988:keven # group:password:gid:members

Time

• stat [file]

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mtime : modified time, last write
atime : access time, last read
    depends on mount options:
        relatime : update atime not every read
        noatime : don't update atime
ctime : change time, last metadata write or last data write
btime : creation/birth time, first created

Environment variables

• export [var]=[name] : set an env variable
• echo $[var] : print env variable
• echo $PATH : show system PATH
• export PATH=$PATH:[directory path] : add directory to system PATH
• echo "export PATH=$PATH:[directory path]" >> ~/.bashrc : change the system PATH permanently

SSH

• ssh -p [port] [user]@[ip] : login to SSH
• scp [src path] [user]@[ip]:[dst path] : copy file to remote
  • -p [port] : specify port
  • -r : recursive (directory)
• scp [user]@[ip]:[src path] [dst path] : copy file from remote

Rsync

• rsync -avhzP --delete -e "ssh -p [port]" [src] [user]@[ip]:[dst]
  • -n : dry-run
  • -a : archive, preserve timestamps and permissions
    • might need sudo to preserve permissions
  • -c : compare using checksum
  • --delete : mirror, delete files on dst not in src
  • --ignore-existing : do not overwrite files already in dst
  • -u : only changed files
  • -r : recursive
  • -z : compress during transfer
  • -P : progress and partial transfer
  • -h : human summary
  • --itemize-changes : show file changes summary
  • -v : verbose
  • -vv : very verbose

Network

• ifconfig : show network info
• sudo ss -tulnp : list open ports
  • -t : tcp
  • -u : udp
  • -l : listen only
  • -n : numeric ports instead of names
  • -a : all
  • -p : show process
• sudo iftop -P -f "not udp and not multicast" : list TCP sockets
  • -P : show ports
  • -F "not (ip multicast or broadcast)" : filter out multicast
  • T : show cumulative total
  • t : one line per host
• netstat -natup : list TCP sockets
• nmap -Pn -p- -v [ip] : find open ports

Disk

• lsblk : list disk
• fdisk -l : disk info
• fdisk [disk] : partition disk
• mount [disk name] [directory] : mount disk
• umount [directory] : unmount disk
• cat /proc/mounts : mount info
• cat /etc/fstab : list mounted disks

Info

• fastfetch : system info
• uname -a : show kernel version
• lscpu : list CPU info
• lspci : list PCI devices (Bus:Device.Function)
  • -v : verbose
  • -vv : very verbose
  • -tv : tree
  • -k : kernel modules/drivers in use
  • -n : ID of PCI device (VendorID:deviceID)
• lsusb : list USB devices
  • -v : verbose
  • -t : tree
• nvidia-smi : show GPU info
• du -shc * | sort -rh : show size of files in directory
  • -s : summary
  • -h : human readable
  • -c : show total
  • -b : bytes
  • --apparent size
  • -d [max depth] : max depth
• du -sh [directory] : show size of directory
• df : show disks usage
• free -h --si : show how much RAM
• htop : list process, kill process
• btop : list process, kill process
• sensors : show temperature
• watch -t -n 1 "sensors | grep 'Core 0:'" : show CPU temperature
• strace : trace syscalls
• cat /proc/[pid] : procfs, running processes
• cat /proc/meminfo : memory info
• cat /proc/cpuinfo : CPU info (CPUID)
• cat /proc/interrupts : interrupts in
• cat /proc/ioports : IO ports
• cat /proc/iomem : MMIO
• cat /proc/driver/nvidia/ : GPU info
• cat /proc/stat : all process stats
• cat /proc/[pid]/stat : process stats

Kernel

• lsmod : list kernel modules
  • also cat /proc/modules
• modprobe [module] : load kernel module and dependencies
• insmod [module].ko : install kernel module
• rmmod [module] : remove kernel module
• modinfo -F [info] [module]: get info about kernel module
• dmesg | tail -n 5 : show kernel log
  • -W : show live
• ls -l /dev : list device files
  • major, minor
• cat /proc/devices : list assigned device numbers
• mknod [device] c [major] [minor] : create character device
• rmnod [device]
• head -c 1 [file] : output the first byte of a file

Paths

• . : current directory
• .. : parent directory
• ~ : home directory
• ../relative/path : relative path
• /absolute/path : absolute path

Pipes

• A | B : run A and transfer its output to B
• A & B : run A then B
• A && B : run A then B only if A succeeds
• | grep [some string] : filter out stdout

Redirect

• > : stdout
• < : stdin
• &> : stdout + stderr
• 0> : stdin
• 1> : stdout
• 2> : stderr
• 2>&1 : stderr to stdout, can use cmd | tee out.txt to also print on screen

Bash profile

• ~/.bashrc
  • executed every new shell
• ~/.bash_profile
  • executed once per login
  • inherit ~/.bashrc