To check the present working directory.

ex:pwd

ls

To see content of directory.

ls -l :To see more details including the permissions regarding the contents of directory.

ls -a : to see contents including hidden files of directory.

ls ???* : to see a file whose length is more than 3 characters.

ls –la : To see the file permissions, owners, and sizes of all files, enter:

cat

cat is used to create a file and see the content of file.

cat > filename :to create a file and write content in that.

To append file1 onto the end of file2, enter:

cat file1 >> file2

To view the contents of a file named myfile, enter:

cat myfile

mkdir

Create a directory.

Ex: mkdir directoryname

cd

To change directory.

This command changes the current directory location. By default, the Unix login session begins in the home directory.

(i).To switch to a subdirectory (of the current directory) named myfiles, enter: cd myfiles

(ii).To switch to a directory named /home/wissen/sdm_docs, enter:

cd /home/wissen/sdm_docs

(iii).To move to the parent directory of the current directory, enter: cd ..

(iv).To move to the root directory, enter: cd /

(v).To return to the home directory, enter: cd

rm

This command will remove (destroy) a file. We should enter this command with the -i option, so that we'll be asked to confirm each file deletion.

(i)rm –i filename

(ii).rm –rf <file or Directory>

cp

Copy files from one location to another location.

Ex: cp file1 file2

(i).cp –I file1 file2

mv

Move files from source to destination. and for rename also.

Ex: mv file1 file2

sort

Display the content ascending order.

Ex: sort filename.

head

Display first 10 lines in a file

Ex: head filename

tail

Display last 10 lines in a file

Ex: tail filename

find

The find command lists all of the files within a directory and its subdirectories that match a set of conditions. This command is most commonly used to find all of the files that have a certain name.

Example :To find all of the files named myfile.txt in the current directory and all of its subdirectories, enter:

find . -name myfile.txt -print

To look in the current directory and its subdirectories for all of the files that end in the extension .txt , enter:

find . -name "*.txt" -print

less

This utility displays the contents of a text file one screen at a time, waiting for we to press the Spacebar between screens. This lets we read text without it scrolling quickly off the screen.

Example :To read the contents of a file named textfile in the current directory, enter:

$ less textfile

The less utility is often used for reading the output of other commands.

For example, to read the output of the ls command one screen at a time, enter:

$ ls -la | less

To exit less after viewing the file, press q .

scp

Copy files or directories from one host to another host

rcp

Remote file copy host on network.

Tar

Create Tape ARchives (TAR) and add or extract files.

Ex: tar -cvwf file.tar myfile.txt

Ex: tar -xvwf myfile.tar

nohup

Nohup utility which allows to run command./process or shell script that can continue running in the background after you log out from a shell

nohup command-name &

pscp

This commands is used to copy the files from windows to unix

Syntax: pscp <sourcefile> username@hostname:<destinationpath>

grep

This is used to search a particular pattern(string) in a file

Ex: grep java filename

Ex: ps -ef | grep java àjava related processes are displaying

cmp

This command is used to compare the two files byte by byte.

Ex:cmp file1 file2

We can compare directories also by using cmpdir.

Ex:dircmp -r /home/test1 /home/test2

diff

This command is used to compare the two files line by line.

Ex: diff file1 file2

vi

This is text editor used to create ,edit a file

$ vi filename

To quit without savingà: q!

To save and executeà: x (or): wq

0àmove to the beginning of the line

$-->move to the end of the line

Ctrl-fàscroll forward

Ctrl-bàscroll backward

chsh

To Change shell

Ex: chsh –s ksh <username>

User & User Group Commands

w

Who logged on system what they are doing.

Id

Display current user and group id names.

Who

Displays current logged in user information

Finger

Display current logged in user with full information(including logged time, name)

Users

Print the username of the users currently logged in to the current host

Chown

Changes the owner or group associated with a file.

Ex: Change the owner of /var/run/httpd.pid to 'root'

chown root /var/run/httpd.pid

Disk & Memory Commands

mount

Mounting is done with the mount command

$ mount /dev/fd0 /mnt/floppy

unmount

Unmounting is done with the umount command

umount /mnt/floppy

chmod

To give file permission

Ex: chmod 777 filename

Sar(System Activity Report)

Displays the swap, disk space, I/O, system and cpu status.

Troubleshooting Commands

ps

Displays Running process with PID

· ps - a:

· ps -u:

· ps –ef:

Wall

Displays the contents of a file or standard input to all logged-in users.

telnet

Communicating with other host. Uses the telnet protocol to connect to another remote computer.

Syntax: telnet [ host [ port ] ]

Ex:telnet ipaddress/hostname

History

Displays the list what are the commands you are executed. List of all the commands that you have entered. Each command is given a number according to the order it was entered.

Kill

Terminates a process.

§ kill -9 <process id>

§ Kill -3 <process id>àthis is for thread dump

Ping

Sends ICMP ECHO_REQUEST packets to network hosts.

Ex:ping <ipaddress>

Script

Used to record interactive session.

Ex: script –a –f filename

echo

Displays the variable in the standard out put

Ex: $echo $PATH à Displays Path value

export

Used to set environment variable

Ex: export PATH=<path>

Pidof

Pidof  finds 
the process id (pids) of the named programs.

`Fuser`

      Fuser Displays
the pids of processes using the specified files or file systems

      Ex: fuser
<file name>

            Fuser 
7001/tcp

à

it
will display process id associated with port 7001

`Ifconfig`

Configures or displays network interface parameters for a network using TCP/IP

Nslookup

Queries a name server for a host or domain lookup

Ex: nslookup 204.228.150.3

tracert / traceroute

The traceroute command traces the network path of Internet routers that packets take as they are forwarded from your computer to a destination address

Ex: tracert www.google.com

FAQs (?) :-

What tools or commands are recommended to troubleshoot performance related problems?

A: Following are the basic or essential tools that every Linux or UNIX system admin should be aware of:
a) top
b) sar
c) vmstat
d) iostat
e) free

Command to display the Linux processes in a hierarchical format i.e. Parent and child format

· Process list based on process id -- pstree <PID>

· Process list based on username -- pstree <user name>

How to browse through directory structure

· tree -d will display only the directories. i.e Files will not be displayed.

· tree -a will display hidden files along with directories and files.

· tree -s will display the file size. While using this option, it prints out the size of the files along with the file names.

· tree -p will display the permissions along with the files.

How can we open files having different file formats?

By using “less” we can see the contents of a file

· less filename.pdf

· less filename.doc

· less filename.tar

· less filename.zip

· less filename.iso

· less filename.rpm

How to Find Files Based on Access / Modification / Change Time

You can find files based on following three file time attribute.

Access time of the file. Access time gets updated when the file accessed.

Modification time of the file. Modification time gets updated when the file content modified.

Change time of the file. Change time gets updated when the inode data changes.

min argument treats its argument as minutes.

time argument treats its argument as 24 hours.

Example 1: Find files whose content got updated within last 1 hour

Following example will find files in the current directory and sub-directories, whose content got updated within last 1 hour (60 minutes)

find . -mmin -60

In the same way, following example finds all the files (under root file system /) that got updated within the last 24 hours (1 day).

find / -mtime -1

Example 2: Find files which got accessed before 1 hour

To find the files based up on the file access time, the option -amin, and -atime is used.

find -amin -60

find / -atime -1

Example 3: Find files which got changed exactly before 1 hour

To find the files based up on the file inode change time, the option -cmin, and -ctime is used.

find . -cmin -60

find / -ctime -1

Example 4: Restricting the find output only to files. (Display only files as find command results)

The following find command displays files that are accessed in the last 30 minutes.

find /etc/sysconfig -amin -30

[Note: The above output contains both files and directories]

find /etc/sysconfig -amin -30 -type f

How Do I Make Backups?

A: You can back up a directory hierarchy or complete file system to any media using GNU tar or cpio, the standard *nix tools for this purpose. tar seems to be the more commonly used program currently, and includes command line options to make compressed, incremental, and multi-volume backups.

How Do I Add Temporary Swap Space?

A: In addition to a swap partition, Linux can also use a swap file. Some programs, like g++, can use huge amounts of virtual memory, requiring the temporary creation of extra space. To install an extra 64 MB of swap space, for example, use the following shell commands:

# dd if=/dev/zero of=/swap bs=1024 count=65535

# mkswap /swap

# swapon /swap

The count= argument to dd determines how big the swap file will be. In this example the swap file's name is /swap, but the name and location are, generally, arbitrary, depending only on the file system's available space and your having write permissions in the directory.

When you don't need the swap space any more, remove it with the following statements:

# swapoff /swap

# rm /swap

What Is a core File?

A: A core file is created when a program terminates unexpectedly, due to a bug, or a violation of the operating system's or hardware's protection mechanisms. The operating system kills the program and creates a core file that programmers can use to figure out what went wrong. It contains a detailed description of the state that the program was in when it died.

If would like to determine what program a core file came from, use the file command, like this:

$ file core

That will tell you the name of the program that produced the core dump. You may want to write the maintainer(s) of the program, telling them that their program dumped core.

[Eric Hanchrow]

How To Enable or Disable Core Dumps?

A: By using the ulimit command in bash, the limit command in tcsh, or the rlimit command in ksh. See the appropriate manual page for details.

This setting affects all programs run from the shell (directly or indirectly), not the whole system.

If you wish to enable or disable core dumping for all processes by default, you can change the default setting in linux/sched.h. Refer to definition of INIT_TASK, and look also in linux/resource.h.

How do I find out Linux CPU Utilization?


$ top

$
free –m

OR

$ free –mt

`How to find process id of running program?`

A:

Pidof  finds 
the process id (pids) of the named programs (

Make sure you can see PID of your service)

$ pidof <service-name>

How can we resolve hostname?

A: # dig your-domain.com
# nslookup gw.isp.com

How to find out the total amount of free and used physical and swap memory in the system?

A: $free

What is the command to see whether the host is alive or dead?

A: $ ping <ip-address>

Take thread dump

· Kill -3 <pid>

$ lscpu à It lists cpu architecture information

How to display currently running process?

$ ps -ef

Where

-e to display all the processes.
-f to display full format listing

1.7G total

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