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Audience: Systems Administrators
Last Updated: 5/4/2011 10:34:37 PM
**All times are EST**





Linux Cheat Sheet - Command Line

By Erik Rodriguez

Tags: CentOS cheat sheet, bash cheat sheet, iptables cheat sheet, Linux file paths, Red hat cheat sheet, RHEL cheat sheet

This is a cheat sheet of commonly used commands for Linux operating system. These examples are command line reference for Red Hat and its variants.



COMMAND INPUT

The colors designate the actual Linux command in blue, while the user input (file, numeric value, etc) is red.

Basic Operation

#hostame - Displays the hostname and/or FQDN of the system

#uname -a - Displays the hostname and detailed kernel version

#cat /etc/redhat-release - Displays the version of Linux installed Example:

#cat /proc/cpuinfo - Displays information about the CPU(s)

#df -h - Displays the partitions, their sizes details, and mount points

#free - Displays detail about the system memory and usage

#lsof - Displays all open files

#lsof -nPi:22 - Displays any open files which use port 22

#locate httpd.conf - Displays the full path to any file named httpd.conf

#updatedb - Rebuilds index of files for search using the locate utility

Copy, Move, Delete
#cp file1.txt file2.txt - Copies file1.txt to file2.txt

#mv old.txt new.txt - Renames a file called old.txt to new.txt

#rm file1.txt - Deletes file1.txt

#mkdir httpds - Creates a new directory called httpds

#cp -R httpd httpds - Recursively copies all files from directory httpd to httpds

#cp -PR httpd httpds - Recursively copies all files from directory httpd to httpds and retains all permission settings

#rm -rf httpd - Recursively deletes folder httpd and all contents

#chkconfig --list - Displays all services and their state (start or stop) at each runlevel

#chkconfig --level 35 httpd on - Sets httpd to start on runlevels 35 when machine is booted

#service httpd start - Immediately starts Apache

File Attributes


#chown apache virtualhosts.txt - Changes ownership of the virtualhosts.txt file to user apache

#chgrp apache virtualhosts.txt - Changes membership of the virtualhosts.txt file to group apache

#chmod a+x sniffer.pl - Allows the sniffer.pl file to be executed

CHMOD
7 rwx read, write, execute
6 rw- read, write
5 r-x read, execute
4 r-- read
3 -wx write, execute
2 -w- write
1 --x execute
0 --- no permissions


#chmod 777 passwords.txt - Allows read, write, and execute on the file passwords.txt to anyone

#chmod 000 passwords.txt - Blocks read, write, and execute on the file passwords.txt to anyone

Yum
#yum update -y - Updates all packages without prompting

#yum install iptraf - Installs a package named iptraf

#yum whatprovides */iostat - Searches all repositories and returns RPMs that provide the program iostat

#yum update samba - updates a package named samba

RPM
#rpm -q http - Displays the version of daemon http (apache)

#rpm -qa | grep bind - Displays all packages installed with the word bind. Example:


#rpm -qa | grep bind
bind-chroot-9.3.6-16.P1.el5
system-config-bind-4.0.3-4.el5.centos
bind-utils-9.3.6-16.P1.el5
bind-9.3.6-16.P1.el5
bind-libs-9.3.6-16.P1.el5
ypbind-1.19-12.el5


#rpm -ivh proftpd - Interactively installs proftpd

#rpm -Uvh proftpd - Interactive upgrades named proftpd

#rpm -e proftpd - Removes package proftpd

#rpm --rebuilddb - Rebuilds a corrupt RPM database

Compressed files
#unzip package.zip - Unzips the file package.zip

#tar -zvxf stunnel.tar.gz - Decompressed a gzip file named stunnel.tar.gz

Networking

#ifup eth0 - Enables network interface eth0

#ifdown eth0 - Disables network interface eth0

#vi /etc/sysconfig/network-scripts/ifcfg-eth0 - Uses vi to edit network settings on eth0

IP tables
#service iptables status - Displays status of iptables (running or not)

#iptables -L - Displays ruleset of iptables

#iptables -I INPUT -p tcp -m tcp -s 192.168.15.254/26 --dport 22 -j ACCEPT - Accepts incoming SSH connections from IP range 192.168.15.254/26
#iptables -I INPUT -p tcp -m tcp -s 0.0.0.0/0 --dport 22 -j DROP - Blocks SSH connections from everywhere else

#iptables -I INPUT -s "192.168.10.121" -j DROP - Drops all traffic from IP 192.168.10.121

#iptables -D INPUT -s "192.168.10.121" -j DROP - Removes previously allied drop all from IP 192.168.10.121

#iptables -I INPUT -s "192.168.10.0/24" -j DROP - Drops all traffic from IP range 192.168.10.0/24

#iptables -A INPUT -p tcp --dport 25 -j DROP - Blocks all traffic to TCP port 25

#iptables -A INPUT -p tcp --dport 25 -j ACCEPT - Allows all traffic to TCP port 25

#iptables -A INPUT -p udp --dport 53 -j DROP - Blocks all traffic to UDP port 53

#/etc/init.d/iptables save - Saves all IPtables rules and re-applies them after a reboot




Processes
#ps ax - Displays all running processes

#ps aux - Displays all running processes including CPU and memory usage of each

#ps ax | wc -l - Displays the total number of processes

#top - Interactive process manager which allows sorting by criteria
Logs
#tail -f /var/log/messages - Displays the most current entries to the messages log in real-time

#tail -50 /var/log/messages - Displays the last 50 lines of the messages log

#head -50 /var/log/messages - Displays the first 50 lines of the messages log

#cat /var/log/messages - Displays the entire messages log

#cat /var/log/messages | grep "FTP session opened" - Displays any entries in the messages log that contain the ext FTP session opened

#cat /var/log/messages | grep "FTP session opened" > log2.txt - Writes any entries in the messages log that contain the ext FTP session opened to a file named log2.txt

Paths to Common Files

Bind (named)
/var/named - Bind zone files (non chrooted)
/etc/named.conf - Bind configuration file (non chrooted)
/var/named/chroot/var/named - Bind zone files (chrooted)
/var/named/chroot/etc/named.conf - Bind configuration file (chrooted)

Apache (httpd)
/etc/httpd/conf/httpd.conf - Main apache configuration file
/var/www/html - Default directory for serving pages
/var/log/httpd/ - Default location for logs (access and error)

Networking
/etc/hosts - System hosts file
/etc/resolv.conf - DNS lookup configuration file
/etc/sysconfig/network - Network/hostname configuration file
/etc/selinux - SELinux configuration file
/etc/sysconfig/network-scripts/ - Default location of a network setting file
/etc/sysconfig/iptables - Default iptables policy configuration file
/etc/sysconfig/iptables-config - Default iptables daemon configuration file

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