Basics of Linux - Common Administration Commands

Basic System administration commands along with their purpose:

·         [Updated 7-3-2017]

      Some basic commands that any system administrator will use for the monitoring of systems and day to day administration tasks. Of course there are many many other commands that you can learn and use but you can start from these basic commands and then move forward.

   Disks

df -h :  To check the disk usage/mounted partitions/available space

-h signifies 'Human Readable' so the disk sizes are displayed in MB and GB instead of bytes.

 

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     fdisk -l : list physical disk present and detected by the OS

     *To fix a filesystem on any partition:

e2fsck –b [blocksize] /dev/partitionname for example

e2fsck –b 4096 /dev/sda11

*Do not run the above e2fsck on any mounted partition

iostat: To check the tps of disks, Block reads, Blocks written per second

Sample Output:

·   User Login Info

          To check the current users who are logged in to the machine:

who -r:   To check the run level of machine

who -s:  To check the system load and the uptime of server:

      who -b: To show the boot time of the system

w and uptime:

uptime shows the total uptime of the system. The stats as you may have guessed :P are reset every time you reboot. 

usually instead of using who or uptime, people just use w to get all the info in one go as it shows who's logged in, what process they are currently running the load on the system and the system uptime. So this is one powerful command.

last: To check the last n users logged into server:

Processes 

      To check the memory, swap, top processes:

top

      To check the processes running on the machine and searching for a specific process:

      Standard Syntax

To see every process on the system using standard syntax:

ps -e  

ps -ef 

ps -eF 

ps -ely

 

     BSD Syntax

ps ax (will list all running/sleeping/zombie processes)

ps ax | grep [process] for example to search for ftp

ps ax | grep ftp

·         To check the processor info:

 cat /proc/cpuinfo

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·  Network

dig: Resolve domain names to IP

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ping: test network connectivity and reach of a host

 

traceroute: see hop by hop traversal and performance of a packet to its destination

 

telnet: access a host on a specific port

 

ifconfig: view local ethernet configuration 

  

 

route -n / ip route show

 

Files

To move a specific file from one directory or another:

mv [filename] to /dir/filename

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     To copy a specific file from one directory or another:

cp [filename] to /dir/

·        To copy file from one server to another:

scp [filename] login@machineipaddress:/destinationdir

         To read last [n] lines of files:

tail –n [filename] for example to check the last 200 lines of file:

tail -200f filename

·         To read first[n] lines of files:

head –n [filename] for example to check the first 200 lines of file:

head -200 filename

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