grep HowTo - Linux / Unix Q & A from nixCraft

How to count total number of word occurrences using grep on Linux or Unix

last updated May 29, 2017 in BASH Shell, CentOS, Debian / Ubuntu, FreeBSD, Linux, RedHat and Friends, Suse, UNIX

I want to find out how many times a word (say foo or an IP address) occurs in a text file using the grep command on Linux or Unix-like system?

Linux: Parse an IP Address

last updated January 28, 2011 in Linux

How do I parse my Linux servers IP address using a Bash shell?

CentOS / Redhat: Turn On SELinux Protection

last updated March 31, 2017 in CentOS, Linux, Networking, RedHat and Friends, Security, SELinux

SELinux enforces the idea that programs should be limited in what files they can access and what actions they can take. However, by default it is turned off under RHEL / CentOS 5.x server? How do I turn it on?

Linux: Find Out The Groups A User Is In

last updated July 7, 2010 in Linux

How do I find out group membership for each user? How do I find out which users are in a group called sales?

Linux Find Files By Date And List Files Modified On a Specific Date

last updated August 7, 2018 in BASH Shell, Debian / Ubuntu, Linux, Suse, UNIX

How do I find files by date under UNIX and Linux system? How search for files that created on a specific date on Linux or Unix-like system? How to get a list all files that have been modified on a specific date on Linux or Unix?

Existing lock /var/run/yum.pid: another copy is running as pid 523.

last updated February 23, 2010 in RedHat and Friends

I‘m running the command yum update -y and getting the following error:

Loaded plugins: fastestmirror, priorities
Existing lock /var/run/yum.pid: another copy is running as pid 523.
Another app is currently holding the yum lock; waiting for it to exit…
The other application is: yum-updatesd-he
Memory : 14 M RSS ( 26 MB VSZ)
Started: Tue Feb 9 08:19:02 2010 – 14 day(s) 11:47:39 ago
State : Sleeping, pid: 523
Another app is currently holding the yum lock; waiting for it to exit…
The other application is: yum-updatesd-he
Memory : 14 M RSS ( 26 MB VSZ)
Started: Tue Feb 9 08:19:02 2010 – 14 day(s) 11:47:41 ago
State : Sleeping, pid: 523

How do I fix this problem?

Search Multiple Words / String Pattern Using grep Command on Bash shell

last updated May 14, 2020 in BASH Shell, Debian / Ubuntu, FreeBSD, Linux, RedHat and Friends, Suse, UNIX

How do I search multiple strings or words using the grep command? For example I’d like to search word1, word2, word3 and so on within /path/to/file. How do I force grep to search multiple words? How can I grep for multiple patterns on Linux, OS X, FreeBSD, or Unix-like system? What is the command to search multiple words in Linux?