UNIX Commands
Different types of UNIX commands can be categorized as below:
- Process Commands
- File Commands
- Directory Commands
- Networking commands
- Environmental Commands
- System Admin Commands
Process Commands
- ps – to see all the processes running with your own userid (process status)
- ps -f – to list all information associated with the process run using your own userid.
- ps aux – to display all running processes where a – select all processes on a terminal including those of other users, x- select processes without controlling ttys
- pstree – display tree of a process
- pgrep <string> – it looks through the currently running processes and list the process ids which matches the selection criteria.
- kill – to kill a running process in normal mode
- kill -9 – to kill a running process in abort mode
- top – this command gives system statistics such as system load and the total number of tasks.
- nice – use this command to run a program with certain nice value and it works at the beginning of a new program. For e.g., nice -n 15 abcd_command
- renice – to alter nice value of a command that is already running. For e.g., renice 0 PID_of_pgm
- htop – improved version of top command to get user friendly display.
- jobs – display background and suspended processes.
- osview – displays the operating system statistics
- Ctrl -c – interrupt current process
- Ctrl -z – suspends current process
- bg – send a process to run in background
- fg %jobnumber – bring a running job from back ground to front
File Commands
- ls – list files in a directory
- ls -ltr – long listing of all files in a directory with time stamp
- ls -ltrh – long listing of all files in a directory with time stamp in human readable format of file size
- ls -al – list all files including hidden files in a directory
- cp – copy files
- cp -r – recursive copy of file from a directory
- mv – move a file or other way of renaming a file
- rm -remove a file
- rm -rf – forcefully remove directory and its content
- diff – compare 2 files and shows the difference
- diff -y – shows difference line by line
- wc – tells how many lines, words and characters are there in a file
- chmod – changes read, write, execute permission of files and folders
- chown – change ownership of a file
- chgrp – change group of a file
- gzip – compress files to reduce space
- gunzip – uncompress files compressed by gunzip
- gunzip -c – view the content of gzipped file without opening it
- gzcat – view the content of gzipped file without opening it.
- cat – view the content of a file and show till the end.
- more – view the content of a file one page at a time. You can scroll down a big file but not up with this
- less – view the content of a file. You can scroll up and down the content of a big file which will not fit in one screen.
- head – show the top n lines of file as specified
- tail – shows the bottom n lines of file as specified
Directory Commands
- mkdir – make new directory
- cd – change directory
- pwd – show present working directory
- tar – to compress directory
- rmdir – to remove empty directory
- rm -rf – remove directory with its content
- df – shows free disk space details
- du – shows disk usage
Networking Commands
- ping – test if the machine is reachable
- traceroute – trace the route of packet transfer between source and target host over a network medium
- netstat – displays network connections, routing tables, interface statistics.
- telnet – logon to remote server for transferring file
- ftp – start file transfer protocol window to transfer file to a target server.
- sftp – secure mode of transferring files
- ssh – used for logging in to a remote system with secure encrypted communication between the local and remote system using SSH protocol.
- scp – secure copy of files over network
- get – used for pulling file from a target host
- put – used for placing file in a target system
- wget – download file from a network
- mget – used for pulling multiple files from a target host
- mput –used for posting multiple files to a target system
- hostname- display host/ domain name of the system
- ifconfig – gives the network configuration of the system
- arp – use this address resolution protocol command to see the IP to MAC address translation table if you are having problem in connecting to other hosts
- nslookup – query DNS lookup name
- tcpdump – shows headers of network packets as they arrive in the system
Environmental Commands
- alias – creates a new command
- setenv – list environmental variables
- export – export the parameters for the logged in session. For e.g., export TMOUT=6000 will not disconnect the session till 6000 s
- who – list all users logged in to the same OS and from which terminal
- w – tells who logged in and what they are doing i.e., if they are idle or typing some input from their keyboard
- whoami – list the name of the current user
- which – list the location of executable command
- whereis – list the absolute path of commands
- finger – gives more information of a logged in user
- talk – to have a typed conversation with another logged in user.
- last – tells you when the user last logged on and off and from where.
- Id – list the userid
- date – show date of the current system
- cal – shows calendar
- passwd – allow logged in user to change its own password.
- logout – closes the terminal session
- exit – closes the terminal session
- quota – gives details of disk quota usage
- man – display online reference of each command
- history – display list of command already fired from the same terminal
- grep – searches for lines containing a specified pattern in a file
- awk – used for accessing the rows and columns of a file for data extraction and reporting
- Sed – stream editor utility for editing content of a file
- Cut – used for extracting specific section from each lines of input file
- find – searches for files in directories and sub directories
- locate – find file in system by name
- file – tells about the type of a file
- uptime – shows system uptime
- crontab – used for updating cron entries for scheduling of jobs, scripts
- at – used for single run of scheduling of jobs
- vi – opens a vi editor
System Admin Commands
- usermod – modify attributes of an existing user account.
- userdel – delete an existing user account
- useradd – adds a new user account in the system
- groupadd – adds a group to the system
- groupmod – modifies the group of an existing user account
- groupdel – delete an existing group
- chown – change ownership of a file
- osview – display operating system statistics.
- lsof – show list of open files
- sudo – use this command to run any command as the superuser root.
- mount – mount a file system
- umount – unmount a file system
- shutdown – brings the system down
Read more on UNIX Processes
Read more on UNIX Architecture