At Shell Prompt¶

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

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 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 command prompt:
```
CRTL + w
```
Delete single word on command prompt
```
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

Networking

Shows the network connections
```
$ ifconfig
```
Show ip address for all available interfaces
```
$ ip addr | grep inet
```

Find which process owns port number:

    $ fuser -v -n tcp <port_number>

**Usage**: fuser -v -n tcp 6000

List used ports

    $ lsof -i <protocol>:<port>;

**Usage**: lsof -i tcp:80

check is apache reading 80 or not

Get blocks and partitions

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

Swap

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

dd

Create file of 1 TB file with 8192 blocksize:

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

curl

Post data using curl:

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