xsos – a tool for sysadmins and support

Here is a very nice article that you may find useful

https://access.redhat.com/discussions/469323

ssh – remove offending key.

Whenever a system/server is re-installed or the host key changed for any reason, you would have seen the “host key verification failed”. And as usual you would have to go to known_hosts file and delete the offending key. I will show you 2 simple ways to do this here.

The output that you get in such scenario is:

Offending ECDSA key in ~/.ssh/known_hosts:4

First, you can use sed to directly delete the offending key with a command like this :

How to verify sha256sum for multiple file or one file.

So, lets say you have downloaded the SHA256SUMS files. This file contains the sha256sum for multiple files and you want to compare the values for only one or some of them, then the simplest thing you can do is:

sha256sum -c SHA256SUMS

Now, with this if you do not have some files present then you might get some errors and if you do not want that, then you can try this:

Executing commands on multiple hosts

If you have to execute the same command in multiple hosts, then you can use mussh:

Description : Mussh is a shell script that allows you to execute a command or script

over ssh on multiple hosts with one command. When possible mussh will use

ssh-agent and RSA/DSA keys to minimize the need to enter your password

more than once.

First install mussh with the following command

dnf install mussh

Now to run this for multiple hosts, you can run like this

evvsubst – substitute variables in text in shell

First you need to install gettext, which by the way might be already installed, however you can install with

dnf install gettext

Details of the package:

Name        : gettext

Arch        : x86_64

Epoch       : 0

Version     : 0.19.4

Release     : 4.fc22

Size        : 4.6 M

Repo        : @System

Summary     : GNU libraries and utilities for producing multi-lingual messages

URL         : http://www.gnu.org/software/gettext/

License     : GPLv3+ and LGPLv2+

Description : The GNU gettext package provides a set of tools and documentation for

producing multi-lingual messages in programs. Tools include a set of

conventions about how programs should be written to support message

catalogs, a directory and file naming organization for the message

catalogs, a runtime library which supports the retrieval of translated

messages, and stand-alone programs for handling the translatable and

the already translated strings. Gettext provides an easy to use

library and tools for creating, using, and modifying natural language

catalogs and is a powerful and simple method for internationalizing

programs.

Usage examples:

Easily monitor and archive your system log reports.

If you want to monitor your server logs and also like them to be emailed then just Logwatch may not be sufficient. It sends you a mail but does not archive them, so head over to epylog

Name        : epylog

Arch        : noarch

Epoch       : 0

Version     : 1.0.7

Release     : 9.fc22

Size        : 151 k

Repo        : fedora

Summary     : New logs analyzer and parser

URL         : https://fedorahosted.org/epylog/

License     : GPLv2+

Description : Epylog is a new log notifier and parser which runs periodically out of

cron, looks at your logs, processes the entries in order to present

them in a more comprehensive format, and then provides you with the

output. It is written specifically with large network clusters in mind

where a lot of machines (around 50 and upwards) log to the same

loghost using syslog or syslog-ng.

To install :

ssh authorized keys – limit ssh session to custom command

If you want a ssh key to be able to run a custom command only and nothing beyond that, then you can use the “command” option in the authorized_keys file of ssh.

For example, to limit user to run only top command with a key, you can add the key like this:

echo 'command="/usr/bin/top" ssh-rsa ' >>~/.ssh/authorized_keys