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October 29, 2020

CentOS Commands Cheat Sheet

Operating Systems
Development

If you're just getting started with CentOS, learning the commands and tools is a big help in increasing your productivity. In this blog, we go over some of the most useful CentOS commands and tools as chosen by our enterprise architects, then provide a list of common commands.

Most Useful CentOS Commands and Tools

There are lots of commands when it comes to CentOS and any tool that saves time and provides utility is a welcome addition to any person’s tool kit.

We asked several of our enterprise architects on the team what their favorite tools and commands were and here are some of the results:

1. top

The command top displays a list of processes or threads currently being used by the system kernel. This is useful for telling if something is holding up your systems resources. Summary is the first portion you’ll see followed by the fields and columns header and then the task area. You would use this to determine if a process is hung or hogging all the resources of your system prior to simply killing a pid at random.

2. nmap

Have you ever wondered from a networking perspective, what ports were open on various nodes of your network? Nmap allows you to quickly scan networks for open ports, application version information, running services, what operating system and version, what type of packet filters and firewalls are in use, and plenty of other useful and sensitive information. By listing information such as what ports are open, you can then seal the gaps in your security plan by closing those ports if possible. Nmap is a robust tool and the man pages are a highly recommended read to understand all the options and features available.

3. rpm -ql <packagename> or dpkg -L <packagename>

Have you ever wondered the easiest way to find all the files associated with a particular package? These two commands will show all the files and their location of the package named. Rpm is for RHEL/CentOS and dpkg is for Debian based systems.

4. sosreport

One of the commands we frequently have our customers run during break/fix issues is sosreport. It creates an archive of config and diagnostic data from the system to be used for debugging and troubleshooting later. Can be used with xsos, a tool used to read the reports generated by sosreport.  

5. lsmod

This command arranges and formats the output of modules in /proc/modules and any kernel modules that are currently loaded.

6.tcpdump

An incredibly useful tool that allows you to examine the content of packets on a network interface matching a Boolean expression. This includes such information as handshakes between two devices, logins to sites, server traffic, UDP traffic, requests to printers, but more importantly it can detect traffic going to sketchy destinations or from unknown sources. Has a GUI version known as Wireshark.

 

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Commonly-Used CentOS Commands

While our list above is useful, there are many more commonly-used CentOS commands for Linux that you should keep close by. Here are some that make working from the command line a lot easier.

Directory Movement
CentOS CommandDescription
lslists the contents of the directory
cpcopies a file
mvmoves a directory
cd ..moves up one directory
cd ~moves to home directory
lllists the contents of the directory length-wise
pwdpresent working directory
findsearch given directory for namestring and display it
User Management
CentOS CommandDescription
aliascreates an alias
passwrdupdates user authentication
useraddadds a new user
sudoadmin privileges
whoshows currently logged on users
groupaddcreate new group
unameprint system info
File Management
CentOS CommandDescription
chmodchange permissions of a file
chownchange the ownership of a file
diffcompare the ownership of a file
diffcompare two files against each other
dudisplays disk usage of a directory
rmremoves files/directories
System Management
CentOS CommandDescription
apropossearch set of database files and display result as standard output
bcwiperepeatedly overwrite special patterns onto to-be-destroyed files
chkconfigupdate and query run level info for system services
dstatdisplays real-time system stats
fdiskdisk partioning utility
mountmounts a filesystem
grepsearch named input files for lines containing match to given pattern, then print
hostnameconfigure networking interface
ifdownmanually take down an interface
iftopshows bandwidth usage of interface
ifupbrings interface back up
killterminate a running process
pslist of currently running processes and their process IDs
manmanual page for particular command/tool
systemclmay be used to introspect and control the state of the "systemd" system and service manager
tailused to output last part of a file, useful on log files

Download Our CentOS Commands Cheat Sheet

Want a one-page PDF version of the shortcuts above? Click the link below to download the cheat sheet!

Download Cheat Sheet

Final Thoughts

In conclusion, CentOS is filled with tons of tools and utilities, the aforementioned are just among some of the many available. www.man7.org has manual pages for these, and many more commands and all the usable options that go along with them.

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Talk to an expert today to learn how we can help you with CentOS.

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Additional Resources

Looking for additional information on CentOS? Be sure to check out the resources below!