Sunday, 6 October 2013

Centos 6/RHEL popular commands


One of the greatest attributes of the Minimal Fluxbox Desktop is the key shortcuts to the most used programs and these are certain to include the likes of Thunar and Rxvt terminal emulator or similar. You can use the F1 through 12 keys amongst others to pop up the programs and I assign F1 and F2 to Thunar and Rxvt respectively. 

Notwithstanding the fact that the Minimal Desktop can be made headless by simply hitting Ctrl+Alt+F4, there are also a formidable array of commands at your disposal in order to perform tasks from the console or terminal emulator. Below are some of the most used ones.


The following list describes some of the most useful and popular Linux commands. Consult the man page for each command to learn about additional arguments and details of operation.

# adduser userid

Creates a new userid, prompting for necessary information

# apropos keyword
Searches the manual pages for occurrences of the keyword and prints short descriptions from the beginning of matching manual pages.
 
# at time
 
# at -t file time
 
Executes commands entered via stdin (or, by using the alternative form, the specified file) at the specified time. The time can be specified in a variety of ways; for example, in hour and minute format or in hour, minute, month, day, and year format.
 
# cal month year 

Prints a calender for the specified month of the specified year

Centos 6 calender function
# cat files
 
Prints out the contents of the specified files
 
# cd
 
# cd directory
 
Changes the current working directory to the user's home directory or the specified directory.
 
# chgrp group files
 
# chgrp -R group files
 
Changes the group of the specified files to the specified group. The alternative form of the command operates recursively, changing the group of subdirectories and files beneath a specified directory. The group must be named in the /etc/groups file, maintained by the newgroup command
 
# chmod mode files
 
# chmod -R mode files  
 
Changes the access mode of the specified files to the specified mode. The alternative form of the command operates recursively, changing the mode of subdirectories and files beneath a specified directory.
 
# chown userid files
 
# chown -R userid files 
 
Changes the owner of the specified files to the specified userid. The alternative form of the command operates recursively, changing the owner of subdirectories and files beneath a specified directory.
 
# clear
 
Clears the terminal screen
 
# cp file1 file2

# cp files directory
 
# cp -R files directory
 
Copies a file to another file or directory, or copies a subdirectory and all its files to another directory.
 
# date
 
# date date
 
Displays the current date and time or changes the system date and time to the specified value.
 
# df
 
Prints the amount of free disk space on each mounted filesystem
 
# diff file1 file2 

# Compares the two files, reporting all discrepancies. Similar to the diff command though the output format differs.
 
# dmesg
 
Prints the messages resulting from the most recent system boot
 
# du
 
# du directories 

Prints the amount of disk space used by the current directory (or the specified directories) and subdirectories.

# echo string

# echo -n string

Prints the specified text on the standard output stream. The -n option causes omission of the trailing newline character.
 
# fdformat device 

Formats the media inserted in the specified floppy disk drive. The command performs a low-level format only; it does not create a filesystem. To create a filesystem, issue the mkfs command after formatting the media.

# fdisk device

Edits the partition table of the specified hard disk.

# fg

# fg jobs

Brings the current job (or the specified jobs) to the foreground.

# file files

Determines and prints a description of the type of each specified file.
 
# find

# find path -name pattern -print

Search for files in a directory hierarchy. Searches the specified path for files with names matching the specified pattern (usually enclosed in single quotes) and prints their names.
 
# finger users 
 
Prints a description of the specified users (install with yum).
 
Centos 6 Finger command

# ftp hostname

Opens a FTP connection to the specified host, allowing files to be transfered. The FTP program provides subcommands for accomplishing file transfers.

# grep pattern files
 
# grep -i pattern files
 
# grep -n pattern files
 
# grep -v pattern files 
 
Search the specified files for text matching the specified pattern (usually enclosed in single quotes) and print matching lines. The -i option specifies that matching is performed without regard to case. The -n option specifies that each line of output is preceded by the file name and line number. The -v option reverses the matching, causing non-matched lines to be printed.

# gzip files

# gunzip files

Compress (or expand) the specified files. Generally, a compressed file has the same name as the original file, followed by .gz.
 
# head files
 
Prints the first several lines of each specified file.
 
# hostname
 
# hostname name
 
Displays (or sets) the name of the host.

# info

Launches the GNU Texinfo help system.

# init run_level (eg '3')

Changes the system run level to the specified value

# insmod module

Dynamically loads the specified module

# jobs

Displays all background jobs

# ispell files

Checks the spelling of the contents of the specified files

# kill process_ids

# kill -l

Kills the specified processes, sends the specified processes the specified signal (as a number or a name), or prints a list of available
 
# killall program
 
Kills all the processes that are instances of the specified program or sends the specified signal to all processes that are instances of the specified program.

# ispell files

Checks the spelling of the contents of the specified files

# ln old new

# ln -s old new

Creates a hard (or soft) link associating a new name with an existing file or directory.

# locate pattern

Locates files with names containing the specified pattern and uses the database maintained by the updatedb command.

# lpq

Prints the entries of the print queue

# lpr files

Prints the specified files

# lprm job

Cancels printing of the specified print queue entries. Use lpq to determine the contents of the print queue.

# ls

# ls files

# ls -a files

# ls -l files

# ls -lr files

Lists (non-hidden) files in the current directory or the specified files or directories. The -a option lists hidden files as well has non-hidden files. The -l option causes the list to include descriptive information, such as file size and modification date. The -R option recursively lists the subdirectories of the specified directories.
 
# mail
 
Launches a simple mail client that permits sending and recieving email messages. 

# man title

# man section title

Prints the specified man page.

# mkdir directories

# mkdir -p directories

Creates the specified directories. The -p option causes creation of any parent directories needed to create a specified directory.
 
# mkfs -t type device 
 
Creates a file system of the specified type on the specified device.

# mkswap device
 
Creates a Linux swap space on the specified hard disk partition.

# more file
 
Lets the user peruse a file too large to be displayed as a single screen (page) of output. The more command provides many subcommands that let the user navigate the file. For example, the Space key moves forward one page, the b key moves back one page, and the q key exits the program.

# mount

# mount device directory

# mount -o option -t device directory
 
Prints the mounted devices or mounts the specified device at the specified mount point. (usually a sub-directory of /mnt).
The mount command consults /etc/fstab to determine statndard options associated with a device. The command generally requires root privileges. The -o option allows specification of a variety of options. For example, ro for read-only access. The -t option allows specification of the filesystem type (eg ext2, msdos etc)
 
# mv paths target
 
Moves the specified files or directories to the specified target.
 
# newgroup 

Creates the specified group

# passwd

# passwd user
 
Changes the current user's password, or that of the specified user (reaquires root privileges). The command prompts for the new password.
 
# ping host
 
Sends an echo request via TCP/IP to the specified host. A response confirms that the host is operational.
 
# pr files
 
Formats the specified files for printing, by inserting page breaks and so on. The command provides many arguments and functions.
 
# ps
 
# ps -Aux
 
Display the processes associated with the current userid or displays a description of each process.
 
# pwd
 
Prints the absolute path corresponding to the current working directory. 

# reboot

Reboots the system.

# reset

Clears the terminal screen and resets the terminal status.

# rm files

# rm -i files

# rm -f files

# rm -if files

# rm -rf files

Deletes the specified files or (when the -r option is specified) recursively deletes all subdirectories of the specified files and directories. The -i option causes the command to prompt for confirmation; the -f option suppresses confirmation. Because deleted files cannot generally be recovered, the -f option should be used only with extreme care, particularly when used by the root user.
 
# rmdir directories 

# rmdir -p directories

Deletes the specified empty directories or (when the -p option is specified) the empty directories along the specified path.
 
# shutdown minutes
 
# shutdown -r minutes 

Shuts down the system after the specified number of minutes elapses (requires root privileges). The -r option causes the system to be rebooted once it has shut down.
 
# sleep time
 
Causes the command interpreter to pause for the specified number of seconds
 
# sort files
 
Sorts the specified files. The command has many useful arguments.
 
# split file

Splits a file into several smaller files. The command has many arguments.

# su

# su user

# su -

# su - user

Changes the current userid to root or to the specified userid
The - option establishes a default environment for the new userid.

# swapon device

Enable use of the specified device for swapping

# swapoff device

Enables use of the specified device for swapping

# sync

Completes all pending input/output operations

# tail file

# tail - n file

# tail -f file
 
Prints the last several lines of the specified files. The -n option specifies the number of lines to be printed. The -f option causes the command to continuously print additional lines as they are written to the file.
 
# talk user
 
Launches a program that allows a chat-like dialog with the specified user
 
# tar cvf tar_file files
 
# tar zcvf tar_file files 

Creates a tar file with the specified name, conCreates the specified directories. The -p option causes creation of any parent directories needed to create a specified directory.taining the specified files and their subdirectories. The z option specified that the tar file will be compressed.
 
# tar xvf tar_file
 
# tar zxvf tar_file 

Extracts the contents of the specified tar file. The z option specified that the tar file has been compressed.

# telnet host

Opens a login session on a specified host

# top

Prints a display of system processes that is continually updated until the user presses the q key.

# traceroute host
 
Uses echo requests to determine and print a network path to the host
 
# umount device
 
Unmounts the specified filesystem
 
# uptime
 
Prints the system uptime
 
# w

Prints the current system users

# wall

Prints a message to each user except those who've disabled message reception
 
# traceroute host
 
Uses echo requests to determine and print a network path to the host. 

# wc files

Prints the number of characters, words and lines in the specified files.