MONITORING
OF
LINUX SYSTEM
[1] top : top is a command that neatly list all processes with valuable
info sort by CPU and memory usage.
'top' provides lots of information on the processes running, including the
percentage of the cpu and the memory being consumed by that process, who
'owns' the process and it's pid (Process ID), it also shows the output of
'uptime' and a summary of memory usage, similar to 'free'. The output of
'top' is full screen, and refreshes itself frequently (or at user definable
intervals).
#top
[2] To see last shut down time Of RHEL System:

#last -x|grep shutdown | head -1

[3] To see last reboot history of RHEL System.
#last reboot
[4] W command is use to see the Login Linux user time.
It shows the uptime of the linux system
#w
#w root
[5] netstat -tulpn command to display listening sockets/ports
and associated program.
#netstat -tulpn
[6] control the service :
The ntsysv command is a simple interface for configuring
runlevel services which are also configurable through chkconfig
command. It allows to control which services are
started when the system boots up:
#ntsysv
The rcconf command under Debian / Ubuntu Linux allows you
to control which services are started when the system boots
up or reboots.
#rcconf
[7] uname command :
uname -r: Print the kernel release
#uname -r
uname -v: Showing kernel version:
#uname -v
uname -o : print the operating system
#uname -o
uname -a : print all information
#uname -a
[8] To see list of enable port:
#nmap ‘IP address’
[9] who Command to see who is on the system.
#who
[10] df command to view disk usage and we'll be shown disk usage for
all mounted filesystems in 1K blocks.
#df
Check available space on the hard drive in human readable format.
#df –h
[11] du command:
Now that To know how much space has been used on a filesystem
how can you find out where that data is?
To view usage by a directory or file we can use du. Unless we specify
a filename du will act recursively
Check disk usage for a specific folder:
#du -sh
#du file.txt
1300 file.txt
In human readable format.
#du −h file.txt
1.3M file.txt
[12] free command shows information about the machine's memory.
This includes physical memory (RAM), swap as well as the shared memory
and buffers used by the kernal. All measurements are in Kb.
#free
To see Total RAM with Free avliable.
#free –k
Display shows how much memory is being used in kilobytes,
because we specified the -k option.
#free –m
[13] ps command to see current working process.
#ps
[14] The 'kill' command is complementary to the 'ps' command as it
will allow you to terminate a process revealed with the previous command.
In cases where a process is not responding, you would use the following
syntax to effectively kill it:
‘Kill-9 pid’
where 'pid' is the Process ID (PID) that 'ps' displays for each task.
[15] ls commands:
To see list of all files with hidden files.
#ls -al
To see the largest files on filsystem.
#ls -lS
[16] Finds all files over 20,000KB (roughly 20MB) in size and presents
their names and size in a human readable format:
#find . -size +20000k -exec du -h {} \;
[17] To search the file.
#locate ‘file name ‘
[18] Shutdown the system.
# shutdown −r now.
[19] Reboot the system.
#reboot