Command line hacks

Posted on Sat 12 March 2016 in gnome-terminal

Running previous command with sudo
```
$ ls -la
$ sudo !!
```
Usage: This will run ls -la command using sudo command
Using !! on shell prompt
```
$ ls -la a  && echo !!:2
```
Usage: This will print a on screen.
Finding top 5 largest files in directory
```
$ ls -lSh . | head -5
```
Finding top 5 smallest files in directory
```
$ ls -lSr . | head -5
```
Finding top 10 directories in /
```
$ du -a /var | sort -n -r | head -n 10
```
Finding top directories in /
```
$ du -ch --max-depth 1 /
```
Using !! to replace some part of command
```
$ echo "foo"
$ !!:gs/foo/bar
```
Usage: Runs previous command replacing foo by bar every time that foo appears in previous command

Using !$, !^, !*

$ echo foo bar baz
$ echo !$ # will return baz
$ echo !^ # will return foo
$ echo !* # will return foo bar baz

Press ESC + . to copy last argument of bash command

$ cp /from/same/path/file /to/some/path
$ cd [ESC + . ] # This will take you to /to/some/path

Tail to dmesg
```
$ watch 'dmesg | tail -10'
```
To determine if you have a process holding an unlinked file open
```
$ lsof -a +L1 path_of_directory
```
or
```
$ lsof +D +L1 path_of_directory
```
Find the directory which takes highest space in root
```
$ du --max-depth=1 -h
```

Report XSI interprocess communication facilities status

$ ipcs -s # for seamphore

$ ipcs -q # for message queues

$ ipcs -m # for shared memory segments

Delete till last word in gnome-terminal
```
 CRTL + w 
```
Go to start of line in gnome-terminal
```
CTRL + a
```
Delete single word on gnome-terminal
```
ALT + BACKSPACE
```
Ask Linux to rescan the SCSI devices on that FC HBA
```
$ echo - - - >/sys/class/scsi_host/host$NUMBER/scan
```
Usage: The wildcards “- - -” mean to look at every channel, every target, every LUN.
Taking diff of directory
```
$ diff -bur directory_2 directory_1
```
Executing multiple commands using xargs
```
$ echo 1 | xargs -I{} sh -c "echo {} && echo {}"
```
Usage: Here xargs will take arguments in {}, replace {} in next shell prompt

Force running logrotate configuration file

$ logrotate --force /etc/logrotate.d/nginx

Check permissions of file or directory

$ stat /var/lib/kdcproxy| sed -n '/^Access: (/{s/Access: (([0-9]+).*$/\1/;p}'

Find which process owns port number
```
$ fuser -v -n tcp port_number
```
Usage: fuser -v -n tcp 6000
List used ports
```
$ lsof -i protocol_name:port_number
```
Usage: lsof -i tcp:80 checks apache running on port number 80 or not

Get blocks and partitions

$ egrep -v "#blocks|^$" /proc/partitions|awk '{print $3,  $4}'

More swap with a swap file

$ dd if=/dev/zero of=/swapfile bs=1024 count=65536 #Create 64MB swap file on your root partition
$ mkswap /swapfile 65536          #convert file to swap file
$ sync
$ swapon /swapfile        #add swapfile to your swapspace

Create file of 1 TB file with 8192 blocksize

$ dd if=/dev/zero of=/mnt/disk8 bs=8192 seek=134217728 count=0

Post data using curl

$ curl http://10.209.103.136:443 -d 'hostname=blah' -X POST -v