useful ubuntu/debian commands for sys-Admin

• To clean the cache from system which apt caches when we update/install the packages

apt-get clean

•   To downloads  packages list from repository and update them,to get data on latest available packages

apt-get update

•  To install specific version of  package

apt-get install package-name

• To check OS version   

Ex : lsb_release -a

• To provides the package's description, its dependencies, the name of its maintainer. apt search, apt show, aptitude search, aptitude show work in the similar manner

Ex : apt-cache search php5-fpm

• The checkrestart program tries to determine if there are  processes  in the  system  that  need to be restarted after a system upgrade .Consequently, checkrestart is sometimes used as an audit tool  to  find outdated  versions  of  libraries  in  use, particularly after security upgrades

Ex : checkrestart -h

•  List all installed packages, along with package version and short details.

Ex : dpkg -l php5-fpm

• To check OS version 

Ex : lsb_release -a

• To check memcache version on debian

Ex : telnet localhost 11211;and type 'version'

• To check openssl version on debian

Ex : openssl version -a OR dpkg-query -l | grep openssl

• To know the date on which current version of OpenSSL was built

Ex : openssl version -a OR dpkg-query -l | grep openssl

• To check auto update is enable

Ex : apt-get install unattended-upgrades and look into the files /etc/apt/apt.conf.d/10periodic /etc/apt/apt.conf.d/20auto-upgrades

• To check available packages in Debian/ubuntu

Ex : apt-cache policy openssl

• To check Loaded configuration files in Ubuntu

Ex : php --ini OR php -i | grep 'php.ini'

• To get glibc version

Ex : ldd --version

• To start a daemon at startup

Ex : update-rc.d service_name defaults

• To remove a daemon at startup

Ex : aupdate-rc.d -f service_name remove

• To check apache using which module perfork or worker 

Ex : apache2ctl -l OR apache2ctl -M

• To add CD-rom as repository

Ex : openssl version -a OR dpkg-query -l | grep openssl

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