Next, test with single commands:

pssh -h /path/to/pssh_hosts.txt -A -O PreferredAuthentication

s=password -i “hostname”

pssh -h /path/to/pssh_hosts.txt -A -O PreferredAuthentication

s=password -i “uptime”

The output is:

[root@master pssh]# pssh -h ./pssh_hosts.txt -A -O PreferredAut
hentications=password -i “uptime”
Warning: Do not enter your password if anyone else has superuser
privileges or access to your account.
Password:
[1] 16:27:59 [SUCCESS] [email protected]
21:27:57 up 1 day, 1:30, 1 user, load average: 0.00, 0.01,
0.05

To execute scripts on the target machines, type:

cat pssh/tst.sh

#!/bin/bash
touch /root/CX && echo “File created”

pssh -h ./pssh_hosts.txt -A -O PreferredAuthentications=passw

ord -I<./tst.sh

Now let us make it simple:

pssh -H ‘192.168.100.101’ -l ‘root’ -A -O PreferredAuthentica

tions=password -I< ./tst.sh

The output is:

[root@master pssh]# pssh -H ‘192.168.100.101’ -l ‘root’ -A -O
PreferredAuthentications=password -I< ./tst.sh
Warning: Do not enter your password if anyone else has superuser
privileges or access to your account.
Password:
[1] 16:24:30 [SUCCESS] 192.168.100.101

To execute commands without password prompting, we
need to create a key-pair between the servers. Let us look at
how to do that.
We are trying to attempt to log in to serverB from
serverA.
Create SSH-Kegen keys on serverA, as follows:

ssh-keygen -t rsa

Copy the id_rsa.pub file from serverA to master
serverB:

ssh-copy-id root@

Now try logging into the machine with ssh root@

serverB-IP, and check to make sure that only the key(s)

you wanted were added.

Now, try to use pssh without the password on the

command line.

—Ranjithkumar T., [email protected]

Find out what an unknown command does,

by using whatis

If you are new to the Linux terminal, then you will probably

wonder what each command does. You are most likely to do a

Google search for each command you come across.

To avoid doing that, use the whatis command, followed

by the command you don’t know. You will get a short

description of the command.

Here is an example:

$ whatis ls

ls (1) -list directory contents

Now you’ll know what the command does, and won’t

have to open your browser and search.

—Siddharth Dushantha, [email protected]

Know how many times a user has logged in

One way to find out the number of times users have

logged into a multi-user Linux system is to execute the

following command:

$last | grep pts | awk ‘{print $1}’ | sort | uniq -c

The above command provides the list of users who

recently logged into the system. The grep utility is used to

remove the unnecessary information, the result of which is

then sent to awk using the shell pipe. awk, which is used for

processing text based data, extracts only the user names from

the text. This list of extracted names is now sorted by passing

the list of names to the sort command, through a shell pipe.

The sorted list of names is then piped to the uniq command,

which filters adjacent matching lines, and the matching lines are

merged to the first occurrence. The -c option of the uniq command,

which displays the number of times a line is repeated, gives you

the number of logins of each user along with the user’s name.

—Sathyanarayanan S., [email protected]

Share Your Open Source Recipes!

The joy of using open source software is in finding ways to get

around problems—take them head on, defeat them! We invite

you to share your tips and tricks with us for publication in

OSFY so that they can reach a wider audience. Your tips could

be related to administration, programming, troubleshooting or

general tweaking. Submit them at http://www.opensourceforu.com.

The sender of each published tip will get a T-shirt.

http://www.OpenSourceForU.com | OPEN SOURCE FOR YOU | DECEMBER 2017 | 105