Linux - Cheat Sheet

User management

• useradd [USERNAME] - Add new user
• useradd -G [GROUPNAME][username]- Add new user in group
• passwd [USERNAME] - User account is locked until you set a password with the passwd command
• usermod -a -G [GROUPNAME][username] - Add user in group
• userdel [USERNAME] - Remove the existing user
• cat /etc/passwd | sort - View username and group information
• cat /etc/group | sort - View linux group
• usermod -d -m [NEW_DIRECTORY][username] - Change the user home directory location
• usermod -u [UID][username] - Change the user UID

File Commands

• ls – directory listing
• ls -al – formatted listing with hidden files
• cd <dir> - change directory to dir
• cd – change to home
• pwd – show current directory
• mkdir <dir> – create a directory dir
• rm <file> – delete file
• rm -r <dir> – delete directory dir
• rm -f <file> – force remove file
• rm -rf <dir> – force remove directory dir *
• cp <file1> <file2> – copy file1 to file2
• cp -r <dir1> <dir2> – copy dir1 to dir2; create dir2 if it doesn't exist
• mv <file1> <file2> – rename or move file1 to file2 if file2 is an existing directory, moves file1 into directory file2
• ln -s <file link> – create symbolic link link to file
• touch <file> – create or update file
• cat > <file> – places standard input into file
• more <file> – output the contents of file
• head <file> – output the first 10 lines of file
• tail <file> – output the last 10 lines of file
• tail -f <file> – output the contents of file as it grows, starting with the last 10 lines

Process Management

• ps – display your currently active processes
• top – display all running processes
• kill <pid> – kill process id pid
• killall <proc> – kill all processes named proc *
• bg – lists stopped or background jobs; resume a stopped job in the background
• fg – brings the most recent job to foreground
• fg <n> – brings job n to the foreground

File Permissions

Roles

• u - user (owner of the file)
• g - group (members of file's group)
• o - global (all users who are not owner and not part of group)
• a - all (all 3 roles above)

Numeric representations

• 7 - full (rwx)
• 6 - read and write (rw-)
• 5 - read and execute (r-x)
• 4 - read only (r--)
• 3 - write and execute (-wx)
• 2 - write only (-w-)
• 1 - execute only (--x)
• 0 - none (---)

 1# Add execute for all (myscript.sh)
 2chmod a+x myscript.sh
 3
 4# Set user to read/write/execute, group/global to read only (myscript.sh), symbolic mode
 5chmod u=rwx, go=r myscript.sh 
 6
 7# Remove write from user/group/global (myscript.sh), symbolic mode
 8chmod a-w myscript.sh
 9
10# Remove read/write/execute from user/group/global (myscript.sh), symbolic mode
11chmod = myscript.sh
12
13# Set user to read/write and group/global read (myscript.sh), octal notation
14chmod 644 myscript.sh
15
16# Set user to read/write/execute and group/global read/execute (myscript.sh), octal notation
17chmod 755 myscript.sh
18
19# Set user/group/global to read/write (myscript.sh), octal notation
20chmod 666 myscript.sh

SSH

• ssh <user@host> – connect to host as user
• ssh -p port <user@host> – connect to host on port port as user
• ssh-copy-id <user@host> – add your key to host for user to enable a keyed or passwordless login

Searching (grep, find)

• grep [options] pattern files – search for pattern in files
• command | grep pattern – search for pattern in the output of command
• locate file – find all instances of file
• find [path] [options] [expression]

System Info

• date – show the current date and time
• cal – show this month's calendar
• uptime – show current uptime
• w – display who is online
• whoami – who you are logged in as
• finger <user> – display information about user
• uname -a – show kernel information
• cat /proc/cpuinfo – cpu information
• cat /proc/meminfo – memory information
• man <command> – show the manual for command
• df – show disk usage
• du – show directory space usage
• free – show memory and swap usage
• whereis <app> – show possible locations of app
• which <app> – show which app will be run by default

Compression

• tar cf <file.tar> <files> – create a tar named file.tar containing files
• tar xf <file.tar> – extract the files from file.tar
• tar czf <file.tar.gz> files – create a tar with Gzip compression
• tar xzf <file.tar.gz> – extract a tar using Gzip
• tar cjf <file.tar.bz2> – create a tar with Bzip2 compression
• tar xjf <file.tar.bz2> – extract a tar using Bzip2
• gzip <file> – compresses file and renames it to file.gz
• gzip -d <file.gz> – decompresses file.gz back to file

Network

• ping host – ping host and output results
• whois domain – get whois information for domain
• dig domain – get DNS information for domain
• dig -x host – reverse lookup host
• wget file – download file
• wget -c file – continue a stopped download

Installation

• dpkg -i pkg.deb – install a package (Debian)
• rpm -Uvh pkg.rpm – install a package (RPM)

Install from source

• ./configure
• make
• make install

Shortcuts

• Ctrl+C – halts the current command
• Ctrl+Z – stops the current command, resume with
• fg in the foreground or bg in the background
• Ctrl+D – log out of current session, similar to exit
• Ctrl+W – erases one word in the current line
• Ctrl+U – erases the whole line
• Ctrl+R – type to bring up a recent command
• !! - repeats the last command
• exit – log out of current session