I’ve been working on Linux environment since very long time and recently explored a lot more commands. In this tutorial we will go over some most commonly used Linux Commands for your handy reference.
Let’s get started.
1. How to Get Linux OS version and System Info?
root@crunchify:~# lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 17.04 Release: 17.04 Codename: zesty root@crunchify:/opt# uname -a Linux crunchify 4.9.36-x86_64-linode85 #1 SMP Thu Jul 6 15:31:23 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
2. How to update your OS to latest version?
apt–get update && apt–get upgrade
3. How to create and extract tar.gz?
root@crunchify:/tmp/crunchify# ls -ltra total 12 drwxrwxrwt 10 root root 4096 Oct 6 17:51 .. -rw-r--r-- 1 root root 6 Oct 6 17:51 one.txt drwxr-xr-x 2 root root 4096 Oct 6 17:51 . <!-- Create tar.gz file --> root@crunchify:/tmp/crunchify# tar -cvf - one.txt | gzip > crunchify.tar.gz one.txt root@crunchify:/tmp/crunchify# ls -ltr total 16 -rw-r--r-- 1 root root 6 Oct 6 17:51 one.txt -rw-r--r-- 1 root root 10240 Oct 6 17:52 crunchify.tar.gz <!-- Extract tar.gz file --> root@crunchify:/tmp/crunchify# tar -zxvf crunchify.tar.gz one.txt
4. How to see hidden Linux files?
root@crunchify:/tmp/crunchify# ls -ltra
5. How to symlink a file in Linux?
ln -s /path/to/file /symlink
In below command.. when you type /tmp/java it will be redirected to /opt/java.
root@crunchify:/tmp/crunchify# ln -s /opt/java/ /tmp/java root@crunchify:/tmp# pwd /tmp root@crunchify:/tmp# ls -ltr total 4 drwxr-xr-x 4 root root 4096 Oct 6 18:01 crunchify lrwxrwxrwx 1 root root 10 Oct 6 18:03 java -> /opt/java/
How to forcefully update Symlink? Just use parameter -fs.
6. How to change file permission and owner?
chmod777 <filename>chownroot:root <filename>
Want to apply chmod and chown on directory? Just use parameter -R. Example: chmod -R 777 /folder/.
7. How to remote copy file?
scp crunchify@11.11.11.11:/tmp/crunchify/one.txt /opt/
use parameter -r to copy folder.
8. How to check if Java Process is running?
ps -few | grep java
9.Check since how long my VM is running?
root@crunchify:/tmp/java# uptime 18:12:24 up 34 min, 2 users, load average: 0.08, 0.02, 0.01
10 .How to forcefully generate HeapDump of any Java Process?
$/opt/java/bin> ./jmap -dump:format=b,file=/tmp/heapdump.dmp 33333 (process ID)
11. How to check active number of connections on port 8080 every 5 seconds?
while true; do netstat -an | grep -c $(hostname -i):8080; sleep 5; done;
12. How to login as another user?
sudo su – crunchify
13. How to Download JDK 9 from internet?
Command:
root@crunchify:/tmp/java# curl -L -C - -b "oraclelicense=accept-securebackup-cookie" -O http://download.oracle.com/otn-pub/java/jdk/9+181/jdk-9_linux-x64_bin.tar.gz
Want to install Java using system command?
root@crunchify:/tmp/java# java -version The program 'java' can be found in the following packages: * default-jre * openjdk-8-jre-headless * gcj-4.8-jre-headless * gcj-4.9-jre-headless * gcj-5-jre-headless * gcj-6-jre-headless * openjdk-9-jre-headless Try: apt install <selected package> root@crunchify:/tmp/java# apt install openjdk-9-jre-headless
14. How to empty a big file?
Use command: cat /dev/null > file-name
root@crunchify:/opt# ls -ltr total 16 drwxr-xr-x 3 root root 4096 Oct 6 18:23 java -rw-r--r-- 1 root root 11729 Oct 6 18:32 one.txt root@crunchify:/opt# cat /dev/null > one.txt root@crunchify:/opt# ls -ltr total 4 drwxr-xr-x 3 root root 4096 Oct 6 18:23 java -rw-r--r-- 1 root root 0 Oct 6 18:33 one.txt
15. How to create file without VI or VIM?
Use command touch.
root@crunchify:/opt# ls -ltr total 4 drwxr-xr-x 3 root root 4096 Oct 6 18:23 java -rw-r--r-- 1 root root 0 Oct 6 18:33 one.txt root@crunchify:/opt# touch two.txt root@crunchify:/opt# ls -ltr total 4 drwxr-xr-x 3 root root 4096 Oct 6 18:23 java -rw-r--r-- 1 root root 0 Oct 6 18:33 one.txt -rw-r--r-- 1 root root 0 Oct 6 18:36 two.txt
16. How to see and clear command History?
- root@crunchify:/opt# history (to see history)
- root@crunchify:/opt# history -c (to clear history)
17. General System Information
--------- Free and use memory -----------
root@crunchify:/opt# free -h
total used free shared buff/cache available
Mem: 989M 93M 241M 7.7M 654M 868M
Swap: 511M 0B 511M
--------- system info -----------
root@crunchify:/opt# uname -a
Linux crunchify 4.9.36-x86_64-linode85 #1 SMP Thu Jul 6 15:31:23 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
--------- release info -----------
root@crunchify:/opt# uname -r
4.9.36-x86_64-linode85
--------- find hostname -----------
root@crunchify:/opt# hostname -f
crunchify
--------- Uptime Status -----------
root@crunchify:/opt# uptime
18:41:51 up 1:04, 2 users, load average: 0.00, 0.00, 0.00
--------- find IP -----------
root@crunchify:/opt# hostname -I
74.207.254.177 2600:3c01::f03c:91ff:febd:f028
--------- Check Last Reboot time -----------
root@crunchify:/opt# last reboot
reboot system boot 4.9.36-x86_64-li Fri Oct 6 17:37 still running
wtmp begins Fri Oct 6 17:37:40 2017
--------- find Date -----------
root@crunchify:/opt# date
Fri Oct 6 18:42:09 UTC 2017
--------- Check Calendar -----------
root@crunchify:/opt# cal
October 2017
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31
--------- check who all are online -----------
root@crunchify:/opt# w
18:42:15 up 1:04, 2 users, load average: 0.00, 0.00, 0.00
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root ttyS0 - 17:45 55:23 0.03s 0.02s -bash
root pts/0 216.113.160.67 17:47 7.00s 0.39s 0.00s w
--------- check who you are -----------
root@crunchify:/opt# whoami
root
18. Monitoring and Statistics Commands
------------- Display the last 20 lines of file - and follow it along ------------- root@crunchify:/opt# tail -f one.txt
19. Grep Command – search file
----------- Grep text crunchify from file one.txt ----------- root@crunchify:/opt# grep crunchify one.txt ----------- How to Find files larger than 500MB in /opt --------- find /opt -size +500M ----------- Find files in /opt/java that start with "java" ----------- find /opt/java -name 'java*'
20. Disk space commands
----------- Current directory Disk usage ----------- root@crunchify:/opt# du -sh 875M . ----------- Disk usage in mounted file system ----------- root@crunchify:/opt# df -h Filesystem Size Used Avail Use% Mounted on /dev/root 20G 2.5G 16G 14% / devtmpfs 493M 0 493M 0% /dev tmpfs 495M 0 495M 0% /dev/shm tmpfs 495M 7.7M 487M 2% /run tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 495M 0 495M 0% /sys/fs/cgroup tmpfs 99M 0 99M 0% /run/user/0 ----------- Show inodes stats ----------- root@crunchify:/opt# df -i Filesystem Inodes IUsed IFree IUse% Mounted on /dev/root 1180608 67446 1113162 6% / devtmpfs 126148 1375 124773 2% /dev tmpfs 126633 1 126632 1% /dev/shm tmpfs 126633 1191 125442 1% /run tmpfs 126633 2 126631 1% /run/lock tmpfs 126633 16 126617 1% /sys/fs/cgroup tmpfs 126633 5 126628 1% /run/user/0
21. Understand Linux file Permission
PERMISSION EXAMPLE
U G O
rwx rwx rwx chmod 777 filename
rwx rwx r-x chmod 775 filename
rwx r-x r-x chmod 755 filename
rw- rw- r-- chmod 664 filename
rw- r-- r-- chmod 644 filename
22. Handy Linux Command Cheat Sheet:
Click to expand.
