Essential Linux Commands
| Command | Description |
|---|---|
| pwd | Print current working directory |
| ls | List files and directories |
| ls -l | List with details (long format) |
| cd [directory] | Change directory |
| cd .. | Go up one directory |
| cp [src] [dest] | Copy files or directories |
| mv [src] [dest] | Move or rename files/directories |
| rm [file] | Remove a file |
| rm -r [dir] | Remove a directory and its contents |
| touch [file] | Create an empty file |
| mkdir [dir] | Create a new directory |
| cat [file] | Display file contents |
| less [file] | View file contents page by page |
| head [file] | Show first 10 lines of a file |
| tail [file] | Show last 10 lines of a file |
| grep ‘pattern’ [file] | Search for a pattern in a file |
| find [dir] -name [pattern] | Find files by name |
| chmod [options] [file] | Change file permissions |
| chown [user]:[group] [file] | Change file owner/group |
| df -h | Show disk usage (human-readable) |
| du -sh [dir/file] | Show size of directory/file |
| top | Show running processes |
| ps aux | Show all running processes |
| kill [PID] | Kill a process by process ID |
| man [command] | Show manual/help for a command |
| history | Show command history |
| sudo [command] | Run command as superuser |
Linux Directory Structure (Common Directories Explained)
/ ├── bin # Essential user binaries (commands) ├── boot # Boot loader files, kernel, etc. ├── dev # Device files ├── etc # Configuration files ├── home # User home directories ├── lib # Essential shared libraries ├── media # Mount points for removable media (CD, USB) ├── mnt # Temporary mount points ├── opt # Optional application software packages ├── proc # Kernel and process information (virtual filesystem) ├── root # Home directory for root user ├── run # Runtime data ├── sbin # System binaries (admin commands) ├── srv # Data for services provided by the system ├── sys # System files (virtual filesystem) ├── tmp # Temporary files ├── usr # Secondary hierarchy (user programs, libraries) │ ├── bin # Non-essential user binaries │ ├── lib # Non-essential libraries │ └── share # Shared data └── var # Variable data (logs, spool files, etc.)
Key Points
- / is the root of the whole file system.
- /home/username is your personal directory.
- /etc contains system-wide configuration files.
- /var/log has system log files.
- /tmp is for temporary files (often cleared on reboot).
- /usr holds user programs and data.
Example: Navigating and Listing Directories
pwd # Shows current directory, e.g., /home/user cd /etc # Changes to /etc directory ls /var/log # Lists log files in /var/log
Basic Commands:
| ls | List all files and directories |
| ls -l | List all files and directories with some extra information |
| dir | Display directories |
| mkdir <name> | Create a directory |
| mkidr -p <dir_name1>/<dir_name2> | Create multiple directories |
| rmdir <dir_name> | Remove an empty directory |
| rm <file_name> | Remove a file/directory with confirmation |
| rm -rf <file/dir_name> | Remove file/directory without confirmation |
| cat <file_name> | View a file |
| cat > <file_name> | Create a new file and edit it |
| touch <file_name> | Create a file |
| vi <file_name> | File editor |
| vim <file_name> | File editor |
| command >file_name | Write output of the command into the file |
| cd | Change directory |
| cd .. | Move one directory back |
| cd – | Move to previous directory |
| cd ~ | Move to current user’s home directory |
| cd /home/me | Move to /home/me directory |
| shutdown -h now | Shuts the system down to halt immediately. |
| shutdown -r now | Shuts the system down immediately and the system reboots. |
| mv -i myfile yourfile | Move the file from “myfile” to “yourfile”. This effectively changes the name of “myfile” to “yourfile”. |
| mv -i /data/myfile . | Move the file from “myfile” from the directory “/data” to the current working directory. |
| echo <text> | Display the text |
| find | Search for files in a directory hierarchy |
| grep | Search |
| wc | Word count |
| kill | To kill a process |
| reboot | Reboot the system |
| poweroff | poweroff the system |
| mount | mount a partition |
| umount | unmount a partition |
| fdisk -l | Partition manipulator |
System Informations:
| pwd | Prints present working directory |
| hostname | Prints hostname |
| whoami | Prints your login name |
| date | Prints system date |
| cal <year> | Prints calendar of the year |
| who | Determine the users logged on the machine |
| w | Determine who is logged on the system |
| rwho -a | Determine the remote users |
| finger <user_name> | System info about user |
| last | Show list of users last logged-in on your system |
| lastb | Show last unsuccessful login attempts on your system |
| history | Show the used commands |
| comman | Run the most recent command from the bash history commands that start with the string “ comman “ |
| uptime | Display the system uptime |
| ps | Process status |
| ps -aux | more | List all the currently running process |
| top | List the currently running process, sorted by CPU usage |
| gtop, ktop, htop | GUI choice for top |
| uname | Information of your system |
| arch | Display the system architecture |
| Xorg -version | Show the version of X windows I have on my system |
| cat /etc/issue | Check what distribution you are using |
| free -m | Check your usage, free memory of primary memory |
| df -h | Disk free information in human readable form |
| du / -bh | more | Print detailed disk usage for each sub-directory starting at the “/” (root) directory |
| cat /proc/cpuinfo | Displays cpu information |
| cat /etc/interrupts | List the interrupts in use |
| cat /proc/version | Linux version and other info |
| cat /proc/filesystems | Show the type of filesystem currently in use |
| cat /etc/printcap | less | Show the setup of printers |
| lsmod | Show the currently loaded kernel modules |
| set | more | Show the current user environment |
| env | more | Show environment variables |
| dmesg | less | Print kernel messages |
| chage -l <user_login_name> | See my password expiry information |
| quota | Display my disk quota |
| sysctl -a | more | Display all the configurable Linux kernel parameters |
| runlevel | Print the previous and current runlevel |
Help Commands:
| man <command_name> | Display man pages of the command |
| <command_name> –help | Command help |
| info <command_name> | Helping command |
| whatis <command_name> | Display man pages description |
Compress and Decompress Commands:
| tar –cvf <file_name.tar> <file_name_1> <file_name_2> . . . | Compress files |
| tar –xvf <file_name.tar> | Decompress the compressed file |
| tar –xvf <file_name.tar> – C <location> | Decompress files to desired location |
| tar –zcvf <file_name.tar.gz> <file_name_1> <file_name_2> | Compress files with gz |
| tar –zxvf <file_name.tar.gz> | Decompress the compressed gz files |
| tar –zxvf <file_name.tar.gz> -C <location> | Decompress files to desired location |
apt-get Commands:
| apt-get install <package_name> | Installing package(s) |
| apt-get remove <package_name> | Removing package(s) |
| apt-get update | Update the repository |
| apt-cdrom add | Add CD ROM archives to repository |
| apt-cdrom ident | Identify CD-ROM disk |
| apt-get -d install <package_name> | Download packages, no installation or unpacking |
| apt-get –purge remove <package_name> | Remove all traces of a package, incl. Configuration files etc., |
| apt-get –u update | Upgrades all installed packages, but does not remove any packages to resolve dependencies |
| apt-get –u dist-upgrade | Upgrades all the installed packages, removes or installs packages as needed to satisfy all dependencies |
| apt-cache search <package_name> | Search package in the cache |
| apt-get check | Check broken dependencies |
| apt-cache autoclean | Remove cached packages that are no longer needed |
| apt-cache clean | Remove all cached packages |
| apt-get help | Help |
dpkg Commands:
| dpkg –l | List all the installed packages |
| dpkg –L <package_name> | List files belonging to a package |
| dpkg –S <file_name> | To See which package a file belongs to |
| dpkg –s <package_name> | To show complete package information |
| dpkg –yet-to-unpack | To look for downloaded, uninstalled packages |
| dpkg –audit | Show partially installed packages |
| dpkg -i <package> | Install a new package |
| dpkg -r <package> | Remove a package |
yum Commands:
| yum list [available|installed|extras|updates|obsoletes|all|recent] [pkgspec] | |
| yum list | List packages enabled in the repository |
| yum list all | List packages enabled in the repository |
| yum list available | Lists all the packages available to be installed in any enabled repository on your system |
| yum list installed | Lists all the packages installed on the system |
| yum list extras | Lists any installed package which no longer appears in any of your enabled repositories |
| yum list obsoletes | Lists any obsoleting relationships between any available package and any installed package |
| yum list updates | Lists any package in an enabled repository which is an update for any installed package |
| yum list recent | Lists any package added to any enabled repository in the last seven(7) days |
| yum list pkgspec | Refine your listing for particular packages |
| yum check-update | It returns an exit code of 100 if there are any updates available |
| yum info | Displays information about any package installed or available |
| yum search | Search and list the packages |
| yum provides/yum whatprovides | Searches for which packages provide the requested dependency of file and also takes wildcards for files |
| yum clean | Clean up the cache of metadata and packages |
| yum clean packages | Cleans up any cached packages in any enabled repository cache directory |
| yum clean metadata | Cleans up any xml metadata that may have been cached from any enabled repository |
| yum clean dbcache | Clean up the cached copies of those from any enabled repository cache |
| yum clean all | Clean all cached files from any enabled repository |
| yum shell / yum makecache | These two commands are used to download and make usable all the metadata for the currently enabled yum repos |
rpm Commands:
| rpm –ivh <package_name> | Install a new package |
| rpm –Uvh <package_name> | Update an already installed package |
| rpm –e<package_name> | Remove a package |
| rpm –aq | To list all rpm packages installed on your system |
| rpm –F <package_name> | Freshening up the already installed package |
| rpm –version | Prints rpm version |
Linux Directory Structure:
| /bin | User Binaries |
| /sbin | System Binaries |
| /etc | Configuration Files |
| /root | Root User’s Home Directory |
| /dev | Device Files |
| /proc | Precess Information |
| /media | Removable Media |
| /var | Variable Files |
| /tmp | Temporary Files |
| /usr | User Programs |
| /home | Home Directories |
| /boot | Bootloader Files |
| /lib | System Libraries |
| /opt | Optional add-on Apps |
| /mnt | Mount Directory |
| /srv | Service Data |
Networking Commands:
| ifconfig | Displays all the interface information |
| ifstat | Check the current network usage |
| iptraf | A network utility allows you check the network activities |
| ifup | Bring a network interface up |
| ifdown | Bring a network interface down |
