Linux

iostat = to monitor i/o at disks

mpstat = microprocessor activity

vmstat = virtual memory

netstat = network activity

swapon -s = swap memory usage

top = to view most resource consuming processes

free = to view free space available


$head
is used to display top lines of the file
$head -10 filename

$tail 
to see the last lines of a file

$tail -20 filename

$cal

is used to display calendar

$cal -3 --> displays previous, current and next months calendar

Some usefull files:

/etc/group -> group settings

/etc/hosts -> hostname information

/etc/exports -> it states how partitions are mounted and shared with other Linux/Unix systems.

/etc/fstab -> this file automatically mounts filesystems that are spread across multiple drives

/etc/inittab -> describes which processes are started at bootup or at different runlevels.

/etc/passwd -> contains user information

/etc/shells -> contains the names of all the shells installed on the system

/etc/ftpusers -> contains the login names of users who are not allowed to log in by way of FTP

/etc/shadow -> it contains encrypted passwords are stored in /etc/shadow

/etc/profile -> This file contains settings and global startup info the bash shell

/etc/crontab -> Lists commands and times to run them for the cron deamon

/var/log/messages -> The main system message log file

/var/spool/mail -> where mailboxes are usually stored

/etc/resolv.conf -> Configures the name resolver, specifying the address of your name server and your domain name.

/etc/sysconfig/network -> Defines a network interface

/proc/version -> The kernel version

/etc/redhat-release -> Includes one line stating the Red Hat release number and name

vi EDITOR

vi editor is used to make new text files, scripting files or modifying contents of existing files.

modes of vi editor: command mode, execution mode

command mode:

i - to start insertion from current cursor position

I - to start editing from beginning of line

a - to append contents to right side of your current cursor position

A - to append contents to the end of the current cursor line

r - to replace a char from current cursor position

R - to replace a whole word from current cursor position

x - to remove the char from current cursor position

dd - to remove or to delete a line

2dd - to remove 2 lines from current cursor position

yy - to copy the line of current cursor position

2yy - to copy 2 lines from current cursor position

p - to paste the copied content to after cursor position

P - to paste the content above the cursor line

u - to undo previous operations

dgg - to remove or delete above lines including current cursor line till beginning of file

dG - to remove or delete below lines including current cursor line till end of file

l - to move cursor to character by character at a time

h - to move cursor back char by char

k - to move cursor to above line

j - to go to next line

H - to go to end of the file

G - to go to beginning of file

Execution mode

esc - to go to execution mode

:w - to save changes in the file

:q - to quit from the file

:wq - to save and quit

:x - to save and quit

:wq! - Forcibly save changes in the file and quit

:%s/oldtext/newtext/g - to replace all oldtext with newtext in the file

:se no - to display line number

:no se - to hide line number

Partitioning with fdisk

fdisk -l  - to view all available partitions

fdisk -l /dev/sda - view partitions of a specific hard disk 

fdisk -s /dev/sda - to view the size of an existing partition

mkfs.ext3 /dev/sda - after partition is created, format it using the mkfs command

partprobe /dev/sda - It will update in kernel

mount /dev/sda /u03 - mount on a particular directory

Save the /etc/fstab file.(To make partition permanent)

/dev/sda /u03 ext3 defaults 0 0

fsck /dev/sda2 - To repair a corrupted file system.