Looks like you have a problem with your libraries. Does it throw seg error only while executing the above command or does it throw the error for every command executed?
You may need to reinstall the packages that the executed binaries depend upon.
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It's also possible your server has infected binaries for those commands. The infected binaries will sometimes say "seg fault" though in reality the virus/malware is just blocking you from using those commands and/or trying to reinfect a cleaned up server.
I'd recommmend backing up and do an OS reload if that is the case.
if you just type grep and press enter and its shows segmant fault then here i have three things in mind.
1. first update grep package.
2. if not done by (1.) might be your bin directory got some permission problem.
3. if not done by (1.) and (2.) then you need to update and restore those directories by installing/updating packages for your operating system RHEL or CENTOS and then check with rkhunter or chkroot to check out where it shows problem.