Linux Commands – Quick Reference — Articles

Network Configuration

Action — Command
Get IP configuration — ifconfig -a
IP configuration — vi /etc/sysconfig/network-scripts/ifcfg-eth0
Change hostname — vi /etc/sysconfig/network NETWORKING=yes NETWORKING_IPV6=no HOSTNAME=hostname.local GATEWAY=X.X.X.X
Setup a default Gateway — Open /etc/sysconfig/network file: # vi /etc/sysconfig/network GATEWAY=X.X.X.X
Local name resolution — vi /etc/hosts
Configure DNS servers — vi /etc/resolv.conf search uk.aswats.net nl.aswatson.net nameserver 10.128.254.240 nameserver 10.128.254.241
Network interface disable- enable scripts — “/etc/sysconfig/network-scripts” ifdown eth0 ifup eth0
Text-based network configuration tool — system-config-network-tui system-config-network
Restart Network service — service network restart
Manage network interface cards — vi /Etc/udev/Rules.d/70-persistent-net.rules
ping host and output results — ping host
get whois information for domain — whois domain
get DNS information for domain — dig domain
reverse lookup host — dig -x host

VI Commands

Action — Command
Exit VI Save — 😡
Exit VI without Save — :q!
ULN Registration
Proxy — rpm –import /usr/share/rhn/RPM-GPG-KEY up2date –proxy=proxy.uk.aswatson.net:8080
Sysprep tbv ULN — /usr/bin/uuidgen -t Vb: f0dbc569-cd92-4f8d-bf29-9971c3f5721f vi /etc/sysconfig/rhn/up2date-uuid
Change Password — passwd
Delegate persmissions — visudo
Updates installeren (alle) — yum update
Starting & Stopping
Shutdown the system now and do not reboot — shutdown -h now
Shutdown the system in 5 minutes and reboot or now — shutdown -r 5 | now
Reboot — reboot now

Disk and Filesystems

Mount the device cdrom and call it cdrom under the /mnt directory — mount -t iso9660 /dev/cdrom /mnt/cdrom
Mount hard disk “a” as a VFAT file system and call it cdrive under the /mnt directory — mount -t vfat /dev/hda1 /mnt/cdrive
Unmount the cdrom — umount /mnt/cdrom
Executes graphical application for mounting and unmounting file systems — usermount
Mount a CIFS share — 1. Create Mount folder
cd /mnt mkdir <folder> 2. Modify permissions chown <alloweduser> <folder> chgrp <allowedgrp> <folder> 3. Edit Configuration file vi /etc/fstab 4. insert: <server_with_share>:/<share> /mnt/<folder> cifs user=<remoteuser>,domain=<remotedomain>,uid=<localuser>,gid=<localgrp>,password=<localpasswd> 5. Run the mount command mount –a
show disk usage — df
show directory space usage — du

Finding files

Starting with the root directory, look for the file called fname — find / -name fname
Starting with the root directory, look for the file containing the string fname — find / -name ”*fname*”
Find a file called missingfilename (assumes you have already used the command updatedb (see next) — locate missingfilename
Create or update the database of files on all file systems attached to the linux root directory — updatedb
Show the subdirectory containing the executable file called missingfilename — which missingfilename
Starting with the directory called dir, look for and list all files containing textstringtofind — grep textstringtofind /dir
Display the last 10 lines of the system log. — tail -f /var/log/messages
Display the file containing the boot time messages – useful for locating problems. Alternatively, use the dmesg command. — cat /var/log/dmesg

Moving, copying, deleting & viewing files
List files in current directory using long format — ls -l
List files in current directory and indicate the file type — ls –F
List all files in current directory in long format and display in columns — ls –laC
List all files with hidden files — ls -al
Remove a file or directory called name — rm name
Kill off an entire directory and all it’s includes files and subdirectories — rm -rf name
Copy the file called filename to the /home/dirname directory — cp filename /home/dirname
Move the file called filename to the /home/dirname directory — mv filename /home/dirname
Rename files — mv file1 file2
Display the file called filetoview — cat filetoview
Display the file called filetoview one page at a time, proceed to next page using the spacebar — more filetoview
Create directory — mkdir dir
delete directory dir — rm -r dir
force remove directory dir * — rm -rf dir
Delete directory — rmdir dir
force remove file — rm -f file
Change file owner — chown
Change file group — chgrp
Change file protections — chmod
List opened files — lsof
show processes that using the file — fuser filename

Searching

search for pattern in files — grep pattern files
search recursively for pattern in dir — grep -r pattern dir
search for pattern in the output of command — command | grep pattern
find all instances of file — locate file

Yum Install

Display list of updated software — yum list updates
To download and install all updates — yum update
To download and install all Security updates — yum update –security
You can install multiple libraries at once by separating the name of each module with a space. — Yum install software1 software2 etc
Search software — yum search php-
Software info — yum info name

Installing Software

Install the rpm package called name — rpm -ihv name.rpm
Upgrade the rpm package called name — rpm -Uhv name.rpm
Delete the rpm package called Package — rpm -e package
List the files in the package called package — rpm -l package
List the files and state the installed version of the package called package — rpm -ql package
Reinstall the rpm package called name having deleted parts of it (not deleting using rpm -e) — rpm -i –force package
Decompress the files contained in the zipped and tarred archive called archive — tar -zxvf archive.tar.gz or tar -zxvf archive.tgz

User Administration

Create a new user call accountname — adduser accountname
Give accountname a new password — passwd accountname
Log in as superuser from current login — su
At the lilo prompt, start in single user mode. This is useful if you have forgotten your password. Boot in single user mode, then run the passwd command. — linux single
List current processes — ps
Kill a specific process eg. kill 123 — kil 123

Location of Configuration files

List of devices and their associated mount points. — /etc/fstab
Message of the day — /etc/motd
Bash script that is executed at the end of login process. Similar to autoexec.bat in DOS. — /etc/rc.d/rc.local
Conatins full hostname including domain — /etc/HOSTNAME
There are 4 directories that automatically execute all scripts within the directory at intervals of hour, day, week or month. — /etc/cron.*
A list of all know host names and IP addresses on the machine. — /etc/hosts
Paramters for the Apache web server — /etc/httpd/conf
Specifies the run level that the machine should boot into. — /etc/inittab
Defines IP addresses of DNS servers — /etc/resolv.conf
LILO boot loder configuration file. — /etc/lilo.conf
System log daemon (syslogd) configuration — /etc/syslog.conf
SSH client and server configuration files. — /etc/ ssh_config /etc/sshd_config
net time server. — /etc/ntp.conf
File- and print sharing with Microsoft clients. — /etc/smb.conf

File Permissions

If the command ls -l is given, a long list of file names is displayed. The first column in this list details the permissions applying to the file. If a permission is missing for a owner, group of other, it is represented by – eg. drwxr-x—x Read = 4 Write = 2 File permissions are altered by giving the chmod command and the appropriate octal code for each user type. eg Execute = 1 chmod 7 6 4 filename will make the file called filename R+W+X for the owner, R+W for the group and R for others. chmod 755 Full permission for the owner, read and execute access for the group and others. chmod 777 read, write, execute for all chmod +x filename Make the file called filename executable to all users.
Read = 4 Write = 2 — File permissions are altered by giving the chmod command and the appropriate octal code for each user type. eg
Execute = 1 — chmod 7 6 4 filename will make the file called filename R+W+X for the owner, R+W for the group and R for others.
chmod 755 — Full permission for the owner, read and execute access for the group and others.
chmod 777 — read, write, execute for all
chmod +x filename — Make the file called filename executable to all users.

Shortkeys

halts the current command — Ctrl+C
stops the current command — Ctrl+Z
erases the whole line — Ctrl+U
Display list of active X windows — Alt | escape
Start an xterm session — Shift|Control Altx

Printing

LPRng configuration file. — /etc/lpd.conf
Start | Stop the print daemon — /etc/rc.d/init.d/lpd start | stop
Display status of the print daemon — /etc/rc.d/init.d/lpd status
Display jobs in print queue — lpq
Remove jobs from queue — lprm
Printer control tool — lpc
Start X printer setup interface — printtool
Print a file — lpr

Processes

List current processes — ps
Monitor processes — top
Display free memory — free
Terminate process — Kill pid
kill all processes named proc * — killall proc
lists stopped or background jobs — bg
brings the most recent job to foreground — fg
brings job n to the foreground — Fg n

Scheduling Jobs

Schedule a job — at
Schedule repeated jobs — crontab

System info

show current uptime — uptime
display who is online — w
who you are logged in as — whoami
show kernel information — uname -a
cpu information — cat /proc/cpuinfo
memory information — cat /proc/meminfo
show the manual for command — man command
show memory and swap usage — free
show possible locations of app — whereis app
show which app will be run by default — which app
Print the system’s hostname — hostname
display network information — ifconfig

User Management

create an new user — Adduser
create, delete, modify an new user — useradd, userdel, usermod
add, delete or modify group — groupadd, groupdel, groupmod

Sendmail

Config — sendmail.cf sendmail.mc
mail aliases, must run “newaliases” after change. use :include: to include external list in a file. — aliases
mail access control, FEATURE(access_db) should be set in sendmail.mc. For example, in /etc/mail/access cyberpromo.com REJECT mydomain.com RELAY spam@somewhere.com DISCARD — access
list all host/domain accepted for relaying — /etc/mail/relay-domains

NTP

Install the NTP package — yum install ntp
Configure NTP (udp 123) Search for these entries: — # vi /etc/ntp.conf server 0.rhel.pool.ntp.org server 1.rhel.pool.ntp.org server 2.rhel.pool.ntp.org
Start the NTP service and set it to launch automatically upon boot — service ntpd start chkconfig ntpd on
Check NTP peers status — ntpq -p

Secure Copy

Copy a file from a remote host to the local host — scp your_username@remotehost:file.txt /some/local/directory
Copy a file from the local host to a remote host — scp file.txt your_username@remotehost:/some/remote/directory
Copy a directory from the local host to a remote host’s directory — scp -r yourdir your_username@remotehost:/some/remote/directory/yourdir
Copy file from remote host to remote host — scp your_username@host1:/some/remote/directory/file.txt \ your_username@host2:/some/remote/directory/

Webserver

Check if Apche is installed — rpm -qa | grep httpd
Install Apache Webserver — yum groupinstall “Web Server”
yum install httpd
Install PHP Support — yum groupinstall “PHP Support”
yum install php php-mysql
List of useful PHP-libraries and -modules — yum search php-
To see more details about what each module does — yum info name of the module
Start Webserver — service httpd start apachectl start
set the Apache to run automatically when the server boots — chkconfig httpd on
Install LAMP (Linux, Apache, MySQL, PHP) — yum groupinstall “Web Server” “PHP Support” “MySQL Database server” “MySQL Database client” yum install php-mysql
See PHP on the server by creating testpage — vi /var/www/html/info.php <?php phpinfo(); ?> Visit your site: http://server/info.php
Restart Apache — service httpd restart
Scrtipt to control the functioning of the Apache httpd daemon. — apachectl start|stop|restart|fullstatus|status|configtest
Restart / Stop without aborting currently open connections — apachectl graceful |graceful-stop

MySQL

Install MySQL — yum groupinstall “MySQL Database server” “MySQL Database client” or: yum install mysql-server
Start MySQL — service mysqld start
set MySQL to run automatically when the server boots — chkconfig mysqld on
Configure and set MySQL root password (default is empty) — /usr/bin/mysql_secure_installation
Access the MySQL shell — mysql -u root –p mysql
Create and Delete a MySQL Database — mysql> CREATE DATABASE database dbname; mysql> DROP DATABASE database dbname;
Show Databases — mysql> SHOW DATABASES;
Show Users — mysql>select user from mysql.user;
Show Users (avoid duplicate names) — mysql>select distinct user from mysql.user;
To connect remotely bind MySQL port 3306 to your machines IP — vi /etc/mysql/my.cnf #Replace xxx with your IP Address bind-address = xxx.xxx.xxx.xxx or comment out this line to allow all ip’s.
Create user for local/remote logon — mysql>CREATE USER ‘myuser’@’localhost’ IDENTIFIED BY ‘mypass’; mysql>CREATE USER ‘myuser’@’%’ IDENTIFIED BY ‘mypass’;
Grant permissions on all db’s — mysql>GRANT ALL ON *.* TO ‘myuser’@’localhost’; mysql>GRANT ALL ON *.* TO ‘myuser’@’%’;
Grant permissions on a specific db — mysql>GRANT ALL ON database.* TO ‘myuser’@’localhost’; mysql>GRANT ALL ON database.* TO ‘myuser’@’%’;
Grant all permissions on specific database for specific user — mysql>GRANT ALL PRIVILEGES ON dbname.* TO ‘user’@’%’ IDENTIFIED BY ‘password’
Refresh privileges — mysql>FLUSH PRIVILEGES;
Set Root password — mysql>SET PASSWORD FOR ‘ROOT’@’LOCALHOST” > = PASSWORD(‘new_password’);
Allow Remote ROOT Access (admin Users) — mysql>GRANT ALL PRIVILEGES ON *.* TO ‘root’@’%’ IDENTIFIED BY ‘password’ WITH GRANT OPTION;
Grant access to database for remote IP address — mysql>GRANT ALL ON database.* TO ‘remoteuser’@’remoteIPaddress’ IDENTIFIED BY ‘PASSWORD’;

Firewall

Stop/Start Firewall — service iptables stop|start
Disable/Enable Fiewall — chkconfig iptables off|on
Verifiy Firewall status — service iptables status
Add firewall rule (for example MySQL) — /sbin/iptables -A INPUT -i eth0 -p tcp –destination-port 3306 -j ACCEPT
Add firewall rule for specified source (for example MySQL) — /sbin/iptables -A INPUT -i eth0 -s 10.5.1.3 -p tcp –destination-port 3306 -j ACCEPT
/sbin/iptables -A INPUT -i eth0 -s 10.5.1.0/24 -p tcp –destination-port 3306 -j ACCEPT
iptables -I INPUT 1 -p tcp –dport 443 -j ACCEPT