Linux Admin Zone

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I am putting a damn small thing here regarding bash script for fun.

Here it goes: Need to create a bash script which asks for a word from user, say either “one”, “two” or “three” and then check in single if statement (no else if section) that if its not “one” or “two” or “three” then print Not OK otherwise print OK.

How to run a script per second? Any easy way to check that no multiple instances of the script will run at a single time? I am cnvering 3 simple ways which helps you to fulfill such requirements:

1. Using Cron
   If script needs to be executed every x minute or a frequency which is more than a minute, then it should run through cron only. You can also place it in cron when the script itself contains code to execute repeatedly. Make sure to redirect all its logs/errors to some log file for checking in case some issue occurs.

There are of course various ways to check whether your mail server is now configured ok or not but what I found is that checking through telnet is quick and easy.

let’s check our mail server now, it may be mail.youdomain.com or localhost depending on what you are using right now, here’s the full process:

# telnet localhost smtp
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mail.example.com ESMTP Postfix
mail from: me@example.com
250 2.1.0 Ok
rcpt to: other@example.com
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
Subject: Just a test. 
This is test mail using telnet.  
.
250 2.0.0 Ok: queued as 6846838401D6
quit
221 2.0.0 Bye
Connection closed by foreign host.
#_

here,

# telnet localhost smtp

We are trying connecting localhost on port 25 (smtp). It should get connected and ready to accept your next command

mail from: me@example.com

here you are specifying the sender mail id, it should be a valid mail account otherwise mail server can reject the sender address.

I was amazed to hear from my friend that one of their server got hacked and reason may be that their part-time admin set password of root user as ‘admin’. Wow!! can’t believe it! They dont have right to cry about security attacks as they themselves keep their door opens

I’ve suggested them some points as per described below for ensuring secure access to servers. They have 5-6 Linux servers. This is obviously may not be the best way and I’m as always appreciate if you can give your suggestion in comments. My approach is that from 6 servers, we will be able to login only in 2 servers from remote through key based access and from these 2 server, we can access remaining. Here’s what we did:

Here’s small bash script to backup important log files from a server to a backup server. You should customize it per your environment. I’ve deployed this script in some hosts and its working fine for me but I’m not making any guarantee that this will work for you as well.

Task: Two most important log files in any Redhat based distro is /var/log/secure and /var/log/messages. These are basic log files and there are more log files when your server perform additional roles such as a database server, web server, mail server etc. You can look log files of other installed softwares also and add them in this script to backup them. I have a separate backup server where I want to transfer my log files after compressing them. You can transfer them in some location in case you dont have a separate backup host or environment.