acl at awk bg cheatsheet cli-tools commandline cron crontab cut df disk du environment fg file filesystem grep groupadd groupdel hostname iproute jobs kill linux logging logs memory monitoring nice nohup ownership permission pkill process ps recovery red_hat redirect regex RHCSA root search sed shell shutdown signals sort ss sysadmin systemctl systeminfo tail text_editing text_processing text-processing top truncate uptime useradd userdel usermod variables vi wc wildcards