Hi guys i m just started learning unix .I was working on windows.
Please help me understand it by answering following questions.
How do i find the RAM size for the machine?
What is swap file?
What command are used for log off /Restart and shutdown the linux?

I m using /etc/passwd file for checking user names installed in the machine. is it the correct way?
Do we need to remember different command to do the same task on different unix distributions?

"free -m" will show you summary details of memory usage in Mb.

Swap is a page file, just like on windows. Pages of memory are "swapped" out to disk if necessary.

logout will log you out of a terminal, reboot will reboot and poweroff will turn the power off.

Are above mentioned commands are common for all unix distributions?

No, not necessarily, Might not work on HPUX or other non Linux UNIX systems. Will be fine on most Linux variants though.

Free -m results

total used free shared buffers cached
Mem: 1001 960 40 0 115 517
-/+ buffers/cache: 327 673
Swap: 1983 0 1983


What do you mean by shared buffers cached.
Please explain.

How do i find Total hard drive size for the machine.

command for shutdown and restart are

£ init 0 --------- fr shutdown
$ init 6 ---------- for restart

u can find the above details in /etc/inittab file

u can find all the userinformation and identity from that file /etc/passwd

for checking the hard disk size use this

# fdisk -l | grep Disk

free -m

for seeing the memory in use and free both we use this command
#free -m

for restart the computer in linux is
#reboot
#init 6


for shutting down the computer
#init 0
#poweroff

deepak, I've already said all of that...??? why repeat?

You will find that there are almost always more than one way to do something in unix.

The 'shutdown' command (man shutdown) is more ubiquitous among *nix systems.

Also, a good command to see memory and cpu usage: top

There are some system files for getting this info too (/proc), but best leave that until you are more familiar with the system.

/etc/passwd is the most common place to look for user names on any *nix platform.

Please find the content of inittab file but i m not getting anything out of it what are you trying to suggest please help i want to understand this file.



[root@Test ~]# cat /etc/inittab
#
# inittab This file describes how the INIT process should set up
# the system in a certain run-level.
#
# Author: Miquel van Smoorenburg, <miquels@drinkel.nl.mugnet.org>
# Modified for RHS Linux by Marc Ewing and Donnie Barnes
#

# Default runlevel. The runlevels used by RHS are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault:

# System initialization.
si::sysinit:/etc/rc.d/rc.sysinit

l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6

# Trap CTRL-ALT-DELETE
ca::ctrlaltdel:/sbin/shutdown -t3 -r now

# When our UPS tells us power has failed, assume we have a few minutes
# of power left. Schedule a shutdown for 2 minutes from now.
# This does, of course, assume you have powerd installed and your
# UPS connected and working correctly.
pf:owerfail:/sbin/shutdown -f -h +2 "Power Failure; System Shutting Down"

# If power was restored before the shutdown kicked in, cancel it.
pr:12345owerokwait:/sbin/shutdown -c "Power Restored; Shutdown Cancelled"


# Run gettys in standard runlevels
1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6

# Run xdm in runlevel 5
x:5:respawn:/etc/X11/prefdm -nodaemon

What exactly do you not understand? Please try to ask specific questions

Hint: It causes your system to boot into runlevel 5 and start a display manager using "prefdm" (which I have never heard of)

For more on this file, do "man inittab" in a terminal

man df

Basically swap is similar to page file in windows. but in windows one does not earnark space for it, it just saved in the drive where windows installation resides. And it is often hidden.
But in linux you have to specify seperate disk space for swap and marked the file system as swap while doing the disk partition. As a thumb rule we allocate a space double that of RAM of the computer. When more data or programme is loaded in the memory than the physical memory can handle the system writes some of the data or code on the hard disk. If view the memory usage with system monitor you can see the behaviour of the swaping.

Simplest commands to login and logoff ( on a terminal window) is just:

login <username>
logout - here user name is not required.

Command for shutdown is:

shutdown -h 10 - the system will halt and the process will start after a delay of 10 seconds.
for immediate halt use:

shutdown -h 0

Similarly for restart:

shutdown -r 10 == for 10 sec delay
shutdown -r 0 == for immediate restart.

Commands will be the same among the linux distros, but there may be some variations among other unix types OSes.

These commands are for manual operations on a terminal window. for system automation settings different route has to be followed.

for restart you type restart
for shutdown you type shutdown now
for memory free you type free
for harddisk size you type df -h