Most Used Unix Commands

This post is slightly different from other posts as here I will list down some of the most used unix commands working on all the different aspects.

------------------------------network related----------------------------------- 
ping ip-address
nc -v ip-address port
telnet ip-address port
nslookup hostname
tracert hostname
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ifconfig -a
ifconfig eth0 up
ifconfig eth0 down 

----------------------list files------------------------------------------
ls
ls -ltr
ls -larth
--------------------create file----------------------------------------
touch filename 

------------------empty the contents of the log file----------------------------
cat /dev/null > /var/log/unused.log




----------------------------network file--------------------------------------
vi /etc/resolv-conf

search DOMAIN-NAME.COM
--------------------------------------service command--------------------------------------
Service command is used to run the system V init scripts. i.e Instead of calling the scripts located in the /etc/init.d/ directory with their full path, you can use the service command.

service ssh status
service --status-all
service ssh restart

service iptables status
----------------------------------------Mount ------------------------------------------------------
mount -t nfs <SERVERNAME>:/SERVER_PATH /LOCAL-PATH

-------------etc/fstab example----------------------------------------

/etc/fstab

SERVER-NAME:/SERVER-PATH /LOCAL-MACHINE-PATH    nfs    vers=3,proto=tcp,hard,intr,timeo=600,wsize=65536,rsize=65536

chown -R oracle:oracle /LOCAL-DIR-PATH/
chown user:group filename 
chmod -R 775 /LOCAL-DIR-PATH/

----------copy a folder recursively-------------------------------------- 
cp -R folder1 folder2
Copy file1 to file2 preserving the mode, ownership and timestamp.

$ cp -p file1 file2

--------------tar gz a folder-----------------------------------------------

cd /u01
tar -zcvf app.tar.gz app
tar -zxvc app.tar.gz 

---------------------------remove a folder and contents------------------------
rm -rf folder
rm file 

------------search for a pattern inside a file------------------------------

grep -R pattern filename
grep  1024 . -R


-----------find file--------------------------------------------------------
locate filename
find . -name filename 

-----------------------to set the hostname correctly----------------------------
vi /etc/hostname
vi /etc/hosts 

--------------------------search for the processes--------------------------

ps -ef | grep java

ps -efH | more (hierarchy)

kill -9 process-id 

--------------------------network related- update the network information----------------

cd /etc/sysconfig/networkscripts
vi ifcfg-eth0 

ifup eth0
ifdown eth0

-----------------------------------set the default domain to search-----------------------

vi /etc/resolv-conf

search DOMAINNAME.COM

-------------------iptables--------------------------------------------------------------
service iptables status
service iptables stop
service iptables start


----------------find files more than 200 mb----------------------------------------
cd /apps/Oracle
find . -type f -size +200000k -exec ls -lh {} \; | awk '{ print $9 ": " $5 }'

------------find files more than 5 days old and remove----------------------

find . -mtime +5 -name *.log

find . -mtime +5 -name *.log -exec rm -f {} \; 

-------------------------------------disk space--------------------------
df -T 
df -h
df -ah
df -kh (KB)
df -mh (GB)

-------------------superuser---------------------------------------------
su
sudo su

su - USERNAME
sudo command

-----------------memory related----------------------------------------
top
free/Free
msptat
sar
vmstat
lsof
tcpdump -i eth0
netstat -a | more
netstat -an | grep port-number (to see if the port is open and listening)
htop
iotop
iostat
IPTraf

--------------------less---------------------------------------------------
less filename
g firstline
G lastline
/text forward-search
?text backward-search
n next search match
N previous search match
spacebar nextpage
b previous page
arrows for navigation
<n> G go to line number

----------------Environment edits------------------------------------------
vi ~/.bashrc
vi ~/.bash_profile

--------------Set Environment variables--------------------------------------
export JAVA_HOME=/usr/java/jdk1.8
export PATH=$JAVA_HOME/bin:$PATH


---------------------find the difference between 2 files----------------------------
diff file1 file2

----------------------disk usage------------------------------------------------------
go to the folder and issue
du -kh
du -mh
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----------------------------download file from internet----------------------------------

wget http://server/file.gz

--------------------------------------------------------------------- 

------------------YUM and RPM---------------------------------------

rpm -ivh
rpm -uvh
rpm -ev


yum install httpd
yum update httpd
yum delete httpd

-------------------------------------------------------------------------------------------------
Print N number of lines from the file named filename.txt

$ tail -n N filename.txt
--------------------------------------------------------------------------------------------------

---------which & whereis--------------------------------------
whereis zip
which zip
--------------------------------------------------------------------

Uname command displays important information about the system such as — Kernel name, Host name, Kernel release number,
Processor type, etc.,

uname -a

-----------------------password related-----------------------------------------------------------

change your password from command line using passwd. This will prompt for the old password followed by the new password.

$ passwd

Super user can use passwd command to reset others password. This will not prompt for current password of the user.

# passwd USERNAME

Remove password for a specific user. Root user can disable password for a specific user. Once the password is disabled, the user can login without entering the password.

# passwd -d USERNAME

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Give full access to user and group (i.e read, write and execute ) on a specific file.

$ chmod ug+rwx file.txt
Revoke all access for the group (i.e read, write and execute ) on a specific file.

$ chmod g-rwx file.txt

Apply the file permissions recursively to all the files in the sub-directories.

$ chmod -R ug+rwx file.txt
-------------------------------------------------------------------------------------------------------------
free command is used to display the free, used, swap memory available in the system

free
free -g (gb)
free -t (swap)

---------------------------------------------------------------------------------------------------------------
Machine restart shut
init 0
init 6

shutdown -h now (Shutdown the system and turn the power off immediately)

shutdown -r now (Reboot the system using shutdown command) 

-------------------------Unzip

unzip file.zip

unzip -l file.zip (to view the contents only )

--------------------------------------------------------------------------- 

------------------------------------------------gzip -----------------------------------------------------------------
gzip file.txt (To create a *.gz compressed file)
gzip -d file.gz (To uncompress a *.gz file)

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grep -r "Error" * (Search for a given string in all files recursively)
grep -i "Exception" demo_file (Search for a given string in a file (case in-sensitive search))
find ~ -empty (Find all empty files in home directory)
find -iname "MyCProgram.c" -exec md5sum {} \; (Execute commands on files found by the find command)

--------------run a command forever------------------------------------------------------------------

watch -n5 "telnet host port" (watch command will repeat a command forever with an interval specified)
every 5 seconds
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remote working

ssh username@machinename

scp username@machinename:/dir/filename username@machinename:/dir/filename


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Also if you used a command once and then want to re-issue again without trying to remember the whole command just search the history


history | grep tail
history | grep telnet
history | grep ping


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Formatting

mount | column –t


cat /etc/passwd | column -t -s

Repeat a Command Until It Runs Successfully

while true

Sort Processes by Memory Usage

ps aux | sort -rnk 4

Sort Processes by CPU Usage


ps aux | sort -nk 3

Watch Multiple Log Files at the Same Time

use multitail

Monitor Command Output at Regular Intervals

watch df -h

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Sudo requires that you type your own password. (The purpose is to limit the damage if you leave your keyboard unattended and unlocked, and also to ensure that you really wish to run that command and it wasn't e.g. a typo.) It is often configured to not ask again for a few minutes so you can run several sudo commands in succession.

$ sudo -i
# command 1
# command 2
...
# exit

Instead of sudo -i, you can use sudo -s. The difference is that -i reinitializes the environment to sane defaults, whereas -s uses your configuration files for better or for worse.

su

The su command exists on most unix-like systems. It lets you run a command as another user, provided you know that user's password. When run with no user specified, su will default to the root account.

su -c 'service apache restart'

$ su
# command 1
# command 2
...
# exit