Written By Vivek G. Gite
This
command reference is specially written for the LSST. If you want to get more
information about any of the following command, use man page or info pages as
Syntax:
man
{command-name}
Example:
$ man
cat
Syntax:
info
{command-name}
Example: $
info
date
Even
some command like mv, ls give command help on command line by typing command as
follows
Syntax:
{command-name}
--help
Example:
$ mv --help
$ ls --help | more
To see help or options related with ls command; here you can get screen-by-screen help, since help of ls command is quite big that can't fit on single screen.
NOTE that following commands are for new users or for Beginners only. The purpose is if you use this command you will be more familiar with your shell and secondly, you need some of these command in your Shell script. Latest updated version of this tutorial/document can be found at: http://www.vivek-tech.com/docs/
cat
To
display text file.
Syntax
cat {file name}
Examples
$cat foo
cfdisk*
To
create/modify/delete partition table interactively.
Syntax
cfdisk
cd
To
change current directory.
Syntax
cd {directory
name}
Options
-
(minus) Change to previous directory location.
Examples
$ cd /usr/local/apache
$ pwd
/usr/local/apache
$ cd
/var/log
$ pwd
/var/log
$ cd
–
$ pwd
/usr/local/apache
$
cd (Change to
home directory)
NOTE:
Linux’s $OLDPWD variable holds your last directory setting, if you type
$ cd $OLDPWD, it is same as $ cd -. What happen if you type $ cd – as soon as
you login into Linux?
chfn
Change
the finger information of user.
Syntax
chfn [user-name]
Examples
$ chfn
vivek
$
chfn
# change the currently log on users finger
information
chgrp
Change
the group owner of a file.
Syntax
chgrp {group name} {file/directory name}
Options
-R Recursively change
group owner of files/directory
Examples
chgrp oracle /usr/database
chgrp msc
/home/cstudents
Change
the file/directory permission directory.
Syntax
chmod permission-options file/directory
name.
Options
(a)permission-options
-
rwx rwx rwx
| |
|
1 2 3
1 –
owner
2 –
group
3 –
others
For r,w,x octal value is 4,2,1 respectively.
So if you
want to give r,w,x permission to owner, for group r,x, and for w,x to others.
Then,
rwx
rwx rwx
421
401 021
For
owner add this number as 4+2+1 = 7
For
group add this number as 4+0+1 = 5
For
others add this number as 0+2+1 = 3
So
command will be $ chmod 753
filename
Examples
$chmod 755 first.sh
(b)permission-options -
chmod {u|g|o|a} {+|-} {r|w|x} {filename}
u
- User who owns the file
g - Group file owner
o - User
classified as other
a - All other system user
+
Set permission
- Remove permission
r
- Read permission
w - Write permission
x - Execute
permission
Examples
$ chmod u+x,g+wx,o+x myscript
Above command set permission for file called 'myscript' as User (Person who creates that file or directory) has execute permission (u+x) Group of file owner can write to this file as well as execute this file (g+wx) Others can only execute file but can not modify it, Since we have not given w (write permission) to them. (o+x).
chown
Change
the owner of file/directory.
Syntax
chown {username}[.group-name]
{file/directory-name}
Options
-R
Recursively change
group owner of files/directory
Examples
$chown vivek.users *.jsp
All
files ending with .jsp are now owned by user vivek of the group
users.
clear
Clear
the screen.
Syntax
clear
cp
To
Copy files.
Syntax
cp {source}
{destination}
Options
-f force the cp to copy files
even if file exist (overwrite the files).
-i Ask y/n confirmation before
coping each file.
Examples
$ cp -f /mnt/floppy/*
/home/vivek
cmp
Syntax
cmp {file1} {file2}
Examples
$ cmp myfile myfile.old
date*
Change
or set current date and time.
Syntax
date [date or time string
]
Examples
$date # will show current date
& time
$date --date=“2001-3-15“ # will set date to
2001-Mar-15
$date --date=“2001-3-15 11:59 AM” # date as well as
time
df
Display
the disk space used file system.
Syntax
df
Options
-m Displays information in
MB.
-k Displays information in
KB.
-h Displays information
in easy-to-understand format.
diff
Display
differences (Comparison between two files) in files.
Syntax
diff {file1} {file2}
dmesg
To display kernel log messages. (Which are shown when your system first time boot)
Syntax
dmesg
du
Displays the disk usage according to space used by file/directory.
Syntax
du [directory
name]
Options
-a all
files
-k Displays information in
KB.
-h Displays information
in easy-to-understand format.
-s Displays only total
not details.
fdisk*
To create/ modify/ delete partition table.
Syntax
fdisk {device
-name}
Options
This are
command of fdisk, you have to use this command after fdisk program
starts.
a Mark bootable
partition.
d Delete
partition.
m Help
n Create new
partition.
p Print partition table on
screen.
q Quit without saving
changes.
t Changes the partition type ID
(type)
w Quit and save changes to
disk.
Examples
$fdisk /dev/hda
find
To Search files.
Syntax
find dirname -name files-to-find -print
Examples
$ find /
-name *.c
-print
finger
Get user information.
Syntax
finger [user-name]
Examples
$finger
$finger
vivek
fsck*
To check the file system for errors, and if found repair it.
Syntax
fsck {device
name}
Options
-f force to repair.
-y Assume “yes” for all questions.
Caution
Do’t run fsck in
multiuser mode, first run system in single mode then un mount file system and
then run the fsck.
Examples
$ init 1 # go to single
user mode or you can type linux
single at
# LILO prompt while booting the system. Note that if
your
#
LILO is password protected, then you have to supply
# password for it.
$
umount /dev/hdx # replace x
with your partition number for e.g
#
umount
/dev/hda1
$ fsck
/dev/hda1
$
reboot
grep
To search text files for particular text.
Syntax
grep “patter-to-search” file-name
Examples
grep “Red Hat” /etc/*
gzip
To compress or decompress file.
Syntax
gzip
file-nane
Options
-d decompress
-S suffix
Examples
$ gzip ltips
$
ls
$ gzip -d ltips
init*
Use to switch between different run-levels.
Syntax
init 0123456
Options
0 halt the
system
1 Single-user
mode
2 Multi-user without NFS
3 Full Multi-user
(Default)
4 Unused
5 Start X windows
6 Reboot
system
Examples
$ su
-l
# init 6 # reboot
# init 1 # single user
mode.
logout
To
login out
Syntax
logout
last/lastlog*
To Display login, telnet and ftp log of your Linux Server.
less
Syntax
less filename
ln
Syntax
ln -s {file/directory}
{file/directory}
Examples
$ln -s
p
longprogname
$ls -l
To quickly (securely also) search file.
Syntax
locate {file name}
Options
-R Recursively display the files & directory.
-l Long listing of files & directory.
Note
If you are running locate first time then run following command, which will create database file. (Run as root user)
$ su
password
#/etc/cron.daily/slocate.cron
Examples
$locate -l foo
ls
Syntax
ls [file/dir
name]
Options
-R Recursively display the files & directory.
-l Long listing of files & directory.
-a Show all files start with . (DOT) # for
e.g.:
.bash_profile
-N Name wise
sorting.
Examples
$
ls
$ ls
-lR / > alist
&
$ ls
–a
mail
Read or send the mail.
Syntax
mail {user-name}
Options
d - Delete the
mail.
q - Quit the mail
program.
s - Save the mail to
mailbox.
$ mail # read
your mail
$
mail
vivek
mount/umount*
Mount/unmount the file system. Useful to work with floppy,cdrom, other (DOS/Windows) partition etc.
Syntax
mount -t {file system type} { device name } {mount point}
Options
-t can be msdos or
vfat
Examples
# must be root user
#To mount your
Cd-Rom
#
mount /dev/cdrom
#
mount –t msdos /dev/fd0 /mnt/floppy
# cd
/mnt/floppy
#
ls
#
mount
# to see all mounted device
more
Syntax
more {file name}
mv
To move the file(s)/directory.
Syntax
mv {source}
{destination}
pr
To print file.
Syntax
pr
{file-name}
Examples
$pr
myfile
passwd
To change the password.
Syntax
passwd
{username}
Options
-d Delete the password. (Use with very carefully)
Examples
$
passwd
ping
Network related command, to verify that network is connected and working properly.
Syntax
ping {host-name | IP
Number}
Examples
$ping www.yahoo.com # if connectd to
Internet
$ping 192.168.1.78
pwd
Print working directory.
Syntax
$
pwd
rpm*
Syntax
rpm {option} {.rpm
file}
Options
-i Install .rpm software.
-U Upgrade the software.
-e Delete the software.
-l List all files in .rpm software package
Examples
$ rpm -i
demo.rpm
rm
Syntax
rm
{filename}
Options
-rf Remove all files/directory with subdirectories. (DOS’s – deltree)
Examples
$ rm foo
$
rm -rf
/home/vivek/oldfiles
sort
To sort files.
Syntax
sort
{file-name}
Options
-r Reverse normal
order
-n Sort
in numeric order
-nr
Sort in reverse numeric order
Examples
$sort
myfile
startx
Start X windows system.
Syntax
startx
Options
Press ctrl + alt +
backspace to kill x windows.
shutdown*
Shutdown linux.
Syntax
shutdown
Options
-r Reboot
Linux.
-h Halt or Shutdown
Example
$shutdown –h now
smbpasswd*
Samba password change.
Syntax
smbpasswd {username}
Examples
$smbpasswd
rani
su*
Become super user if user name is not given, or change the user ID.
Syntax
su [username]
Linux archive program.
Syntax
tar options {tar-file-name}
{dir-name-to-archive}
Options
-c Create the file.
-f {filename} Name of archive
file
-z
Compress the file.
-x
Extract the files from archive
Examples
# To create archive
file of /home/vivek directory
$ tar
-czf
mybackup.tar.gz
/hove/vivek
#If
you want to extract file from above
$ tar
-xf
mybackup.tar.gz
testparm/testprns*
Test the /etc/smb.conf file for errors.
testparm
– To test share setting.
testprns
– To test printer setting.
Above
will also display setting and error if any.
testparm
testprns
top
To see process information in neat format.
Syntax
top
Options
? Get more information about top command.
touch
Create empty file or change/update time stamp of file.
Syntax
touch {filename}
Examples
$ touch
/etc/dhcpd.leases #create
file for dhcpd demon
$ touch
/etc/modules
# update time stamp of file
umask
Specify the permission for files when files are created for owner(u),group(g), and others(o).
Syntax
umask –S {u=xx,g=xx,o=xx}
Where
xx can be (r)ead,(w)rite.
Or you
can use 022 for read only file permission for others and 077 for read and write
permission.
Examples
$umask -S u=rw,g=,o=
$umask 022
useradd/userdel*
Syntax
useradd -g {group-name}
{user-name-to-add}
userdel
{user-name-to-delete}
Examples
#add rani user to
system (must be root)
#adduser -g oracle rani
#passwd
rani
#Delete
the user kaju
#userdel
kaju
w
Shows who logged on and
what they are doing
Syntax
w
who am
i
About your self.
Syntax
who am
i
which
Show the location of file from which it is executed when you type the name.
Syntax
which {file name}
Examples
$ which
cc
$ ls
–l `which cc`
xinit
Initializes X window without loading any windows manager.
Syntax
xinit
Examples
$
xinit
$
kde
* For this command you must be root or root equivalent user.