Linux Commands

Tutorials - Linux Commands

Useful Linux Commands

Linux Help Commands
apropos Apropos keyword - Show all commands with the keyword in their description. The same as the "man -k" command.
help Bash shell help for the bash built in command list. The help command gets help for a particular command.
man Get help from the manual for a command.
man -k keyword - Show all commands with the keyword in their description
"man 2 kill" Display page 2 of the kill command
manpath Determine user's search path for man pages.
info Documentation on Linux commands and programs similar to the man pages but navigation is organized different.

User and Group Management Commands
Chown Change the owner of file(s) to another user.
Chroot Run command or interactive shell with special root directory.
Chsh Change the login shell.
Adduser Ex: adduser mark - Effect: Adds a user to the system named mark
Passwd Set a user's pass word.
Chpasswd Update password file in batch.
W Display users logged in and what they are doing.
Wall Send a message to everybody's terminal.
Who Display the users logged in.
whoami Print effective user id.

APT Package Tool
apt-cache search [package] returns list of packages which corresponds string "searched-packages"
apt-get install [package] install / upgrade a deb package
apt-get update update the package list
apt-get upgrade upgrade all of the installed packages
apt-get remove [package] remove a deb package from system
apt-get check verify correct resolution of dependencies
apt-get clean clean up cache from packages downloaded

Module and kernel management
depmod Handle loadable modules automatically. Creates a makefile-like dependency file.
dmesg Print or control the kernel ring buffer. This shows the last kernel startup messages.
genksyms Generate symbol version information.
insmod Install loadable kernel module.
lsmod List currently installed kernel modules.
modprobe Used to load a set of modules that are marked with a specified tag.
rmmod Unload loadable modules.

File Management
ls Directory listing
ls -al Formatted listing with hidden files
ls -lt Sorting the Formatted listing by time modification
cd dir Change directory to dir
cd Change to home directory
pwd Show current working directory
mkdir dir Creating a directory dir
cat >file Places the standard input into the file
more file Output the contents of the file
head file Output the first 10 lines of the file
tail file Output the last 10 lines of the file
tail -f file Output the contents of file as it grows, starting with the last 10 lines
touch file Create or update file
rm file Deleting the file
rm -r dir Deleting the directory
rm -f file Force to remove the file
rm -rf dir Force to remove the directory dir
cp file1 file2 Copy the contents of file1 to file2
cp -r dir1 dir2 Copy dir1 to dir2;create dir2 if not present
mv file1 file2 Rename or move file1 to file2,if file2 is an existing directory
ln -s file link Create symbolic link link to file

File Permission
chmod -c –R chmod file read, write and executable permission
touch -a –t modify (or create) file timestamp
chown -c –R change file ownership
chgrp -c –R change file group permission
touch -a –t modify (or create) file timestamp

File Compression
bunzip2 file1.bz2 decompress a file called 'file1.bz2'
bzip2 file1 compress a file called 'file1'
gunzip file1.gz decompress a file called 'file1.gz'
rar a file1.rar test_file create an archive rar called 'file1.rar'
rar a file1.rar file1 file2 dir1 compress 'file1', 'file2' and 'dir1' simultaneously
rar x file1.rar decompress rar archive
tar -cvf archive.tar file1 create a uncompressed tarball
tar -tf archive.tar show contents of an archive
tar -xvf archive.tar extract a tarball
tar -xvf archive.tar -C /tmp extract a tarball into / tmp

File Search
find / -name file1 search file and directory into root filesystem from '/'
find / -user user1 search files and directories belonging to 'user1'
find /home/user1 -name \*.c search files with '.c' extension within directory '/home/user1'
find /usr/bin -type f -atime +100 search binary files are not used in the last 100 days
find /usr/bin -type f -mtime -10 search files created or changed within 10 days
find / -name *.c -exec chmod 755 '{}' \; search files with '.c' extension and modify permits
find / -xdev -name \*.c search files with '.c' extension ignoring removable partitions as cdrom, pen-drive, etc.…
locate \*.ps find files with the '.ps' extension - first run 'updatedb' cmd
whereis halt show location of a binary file, source or man
which halt show full path to a binary / executable

cd /home enter to directory '/ home'
cd .. go back one level
cd ../.. go back two levels
cd go to home directory
cd ~user1 go to home directory
cd - go to previous directory
mkdir dir1 create a directory called 'dir1'
mkdir dir1 dir2 create two directories simultaneously
mkdir -p /tmp/dir1/dir2 create a directory tree
mv dir1 new_dir rename / move a file or directory
pwd show the path of work directory
rm -f file1 delete file called 'file1'
rm -rf dir1 remove a directory called 'dir1' and contents recursively
rm -rf dir1 dir2 remove two directories and their contents recursively
rmdir dir1 delete directory called 'dir1'

Memory Related Commands
free -m Display the size of memory in MB
free -b display the size of memory in Bytes.
free -s 5 Update the command for every 5 sec
free –V The -V option, display free command version information.
Ipcs – m shared memory on a linux system
Ipcs – a Shared memory with all details
Memstat -p To identify how much virtual memory is used by the process' associated
/proc/meminfo To check memory usage is to read the /proc/meminfo file
Vmstat - s Memory usage statistics much like the proc command.

Disk Related Commands
Fdisk -l View all Disk Partitions in Linux (fdisk means fixed disk or format disk)
Fdisk -l /dev/sda View Specific partitions
Fdisk /dev/sda Check all available fdisk commands
fdisk –s /dev/sda2 Check the size of specific partitions
mkfs.ext4 /dev/sda4 Format the partitions.
dpkg-query –W show the used space by installed deb packages
du -sh dir1 estimate space used by directory 'dir1'
du -sk * | sort -rn show size of the files and directories sorted by size

Swamp Memory
mkswap /dev/hda3 create a swap filesystem .
swapon /dev/hda3 activating a new swap partitions
swapon /dev/hda2 /dev/hdb3 activate two swap partitions

System Information
arch Print machine architecture.
df Shows disk free space.
du Shows disk usage.
free Display used and free memory on the system.
lsdev Display information about installed hardware via files in the /proc directory.
lsof List open files.
lspci List PCI devices .
procinfo Display system status gathered from proc.
pstree Display a tree of processes.
strace Trace ssytem calls and signals for a binary program.
stty Change and print terminal line settings.
uname Print system information, Prints Linux.
vmstat Report virtual memory statistics.

env Show all environment variables.
export Set the value of a variable so it is visible to all subprocesses that belong to the current shell.
printenv Print all or part of environment.
reset Restores runtime parameters for session to default values.
set Shows how the environment is set up. This is a builtin bash command.

Runtime level management
exit Terminates the shell.
halt Stop the system.
logout Log the user off the system.
poweroff Brings the system down.
reboot Reboot the system.

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