Category Archives: Linux - Page 2

Find all hosts on network with Nmap

To find all pingable hosts on the newtwork you are currently on first find your own ip. In Linux/OSX you can run the command ifconfig (windows uses the ‘ipconfig’ command):

malen@LKGADEFB8:~$ sudo ifconfig
eth0      Link encap:Ethernet  HWaddr 00:1d:7e:ad:ef:b8  
          inet addr:192.168.0.77  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::21d:7eff:fead:efb8/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:23647854 errors:0 dropped:83 overruns:0 frame:0
          TX packets:31522391 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:320343317 (305.5 MiB)  TX bytes:3340057852 (3.1 GiB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:1736 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1736 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:159128 (155.3 KiB)  TX bytes:159128 (155.3 KiB)

You here see your IP at ‘inet addr’ on eth0: 192.168.0.77. To see if there are any other hosts on the 192.168.0.x net use:

nmap -v -sP 192.168.0.1/24

This will ping all hosts on 192.168.0.x and show your result in a list

Host 192.168.0.1 appears to be down.
Host 192.168.0.2 appears to be down.
Host 192.168.0.3 appears to be down.
Host 192.168.0.4 appears to be down.
Host 192.168.0.5 appears to be down.
...
Host Slug (192.168.0.77) appears to be up.
...
Host 192.168.0.250 appears to be down.
Host 192.168.0.251 appears to be down.
Host 192.168.0.252 appears to be down.
Host 192.168.0.253 appears to be down.
Host 192.168.0.254 appears to be down.
Host 192.168.0.255 appears to be down.

Tested on OSX 10.7.4 and Debian Lenny

Send mail from command line

Sending mail directly from a Linux server can often be handy. Here is how I do it

Send mail

cat "Test" | mail -s "Test subject" someone@someplace.com

This will send a mail with the message “Test” and subject line “Test subejct” to email adress: someone@someplace.com

Send attachments

mutt -s "Attachment subject" -a attachment.jpg someone@someplace.com

This will open up your favorite editor so you can create a mail message to your attachment. After you save and exit the editor you just press ‘y’ to send the message with the attachment (you will be inside Mutt then)

Tested on RHEL 3

Remove files in batches of x files

Every now and then I try to do things on a large amount of files – this often ends in a command error about “Too many files” or something similar. One solution to this is to send batches of information to the command instead of sending all at once.

Here is an example on how to delete files in batches of 1000 files:

ls | xargs -n 1000 rm -v

The trick here is the -n 1000 that will send the result from the ls command in batches of a 1000 results per time until the ls list is empty to rm. Neat ah? 🙂

Tested on RHEL 3