Linux Support ~ Pakistan is a Great Country

USEFUL COMMONDS FOR LINUX ADMINISTRATION

uptime

This command displays a one line summary showing...
Example:- [root@akwal]# uptime
09:51:14 up 2:09, 3 users, load average: 0.38, 0.22, 0.16

last reboot

The top row show you last reboot or uptime

who

This command will display...

All users logged in
tty device(line) they are using
When they logged in
Idle time
Where they logged in from
Example:- [root@akwal]# who

id

This command displays a one line summary for the current user listing...
user name and number
primary group and number
other groups and numbers

Example:- [root@akwal]# id

uid=1000(roger) gid=100(users) groups=100(users),16(dialout),40(game)
Example:- [root@akwal]# id

free

This command displays statistics on memory usage. The values represent KB's.

Example:- [root@akwal]# free

total used free shared buffers cached
Mem: 63208 61484 1724 27848 1060 49360
-/+ buffers/cache: 11064 52144
Swap: 128516 6500 122016

du

This command stands for disk usage and will print the size of the current directory and subdirectories in 1 KB sizes.
Example:- [root@akwal]# du

df

This command displays information for each file system.
Example:- [root@akwal]# df

env

This command lists all shell (environment) variables and their contents for the current user.
Example:- [root@akwal]# env

ps

This command lists process status. There are many options for this command. Below are the two most common.
Example:- [root@akwal]# ps

top

This command display a full screen of information of the top processes. It will update automatically until the program is stopped. To stop the display, enter q.

The system, check first the history than the last log-ins, system uptime, last reboot,
history; last ; uptime ; last reboot;

Example:- [root@akwal]# history
[root@akwal]# last

Checking Linux General system info:-

# uname -a;id;uptime;date;free -mtol;who;cat /proc/cpuinfo;echo $PATH;df -m; sysctl vm;

Checking Linux General network configuration info:-

# ip addr show ; ip route show ; ip neigh show; ip rule list; head /etc/resolv.conf
This will show the ip address of the interfaces, the routes, the arp cache , list the routing table rules and our DNS’s.

Monitor the RAM usage of all processes :-

ps -eo pid,ppid,rss,vsize,pcpu,pmem,cmd -ww --sort=pid

Other Specific health checks:-

df -i; cat /proc/mdstats;
df -i checking Inodes state, and /proc/mdstats if we have RAID on the box.

Check for big files and where are the most files on the system:-

for i in *; do echo -n "$i: "; find $i -type f | wc -l; done
-- (count files under directories)
find . -type f -size +30000k -exec ls -lh {} \; | awk '{ print $9 ": " $5 }'
-- (check for files more then 30000kb)