yum - basics

yum – Red Hat tool for RPM package management used to download, install update, erase or list info about system packages

/etc/yum.repos.d/ -> list of configured repositories (web or ftp sites) that will be searched to download and install RPM packages

To view which repositories you have enabled:

yum repolist enabled
repo id -> repo name -> status
InstallMedia -> Fedora 8 -> enabled
fedora -> Fedora 8 – x86_64 -> enabled
updates -> Fedora 8 – x86_64 – Updates -> enabled

Working with yum:

yum install <package_name> -> will search, download and install requested package (e.g.: yum install gcc)

yum update -> will search for available updates and install them to your system

yum check-update -> will look for available updates for your system

yum upgrade -> similar to yum update, but tries to upgrade all your obsolete packages

yum remove (or erase) <packge_name> -> will remove previously installed package and its dependencies (e.g.: yum remove gcc)

yum search <package_name> -> search for package descriptions

yum clean packages -> cleans yum cache in /var/cache/yum/…

yum info <package_name> -> displays info about requested package (similar to rpm -qi) (e.g.: yum info gcc)

For complete options see man page

This is a simple skeleton of a bash countdown script. The script takes two arguments . Here are some examples of its usage:

• countdown time to 90 minutes from now:

./bash-countdown.sh -m 90

• countdown time to 23.3.2036 from now:

./bash-countdown.sh -d "Mar 23 2036"

• countdown time to 21:06 from now:

./bash-countdown.sh -d 21:06

• countdown time to 21:06:45 from now:

./bash-countdown.sh -d 21:06:45

Feel free to modify this script according to your needs:

bash-countdown.sh :

#!/bin/bash 
 
if [ "$#" -lt "2" ] ; then 
	echo "Incorrect usage ! Example:" 
	echo './countdown.sh -d  "Jun 10 2011 16:06"' 
	echo 'or' 
	echo './countdown.sh -m  90' 
	exit 1 
fi 
 
now=`date +%s` 
 
if [ "$1" = "-d" ] ; then 
	until=`date -d "$2" +%s` 
	sec_rem=`expr $until - $now` 
	echo "-d" 
	if [ $sec_rem -lt 1 ]; then 
		echo "$2 is already history !" 
	fi 
fi 
 
if [ "$1" = "-m" ] ; then 
	until=`expr 60 \* $2` 
	until=`expr $until + $now` 
	sec_rem=`expr $until - $now` 
	echo "-m" 
	if [ $sec_rem -lt 1 ]; then 
		echo "$2 is already history !" 
	fi 
fi 
 
 
while [ $sec_rem -gt 0 ]; do 
	clear 
	date 
	let sec_rem=$sec_rem-1 
	interval=$sec_rem 
	seconds=`expr $interval % 60` 
	interval=`expr $interval - $seconds` 
	minutes=`expr $interval % 3600 / 60` 
	interval=`expr $interval - $minutes` 
	hours=`expr $interval % 86400 / 3600` 
	interval=`expr $interval - $hours` 
	days=`expr $interval % 604800 / 86400` 
	interval=`expr $interval - $hours` 
	weeks=`expr $interval / 604800` 
	echo "----------------------------" 
	echo "Seconds: " $seconds 
	echo "Minutes: " $minutes 
	echo "Hours:   " $hours 
	echo "Days:    " $days 
	echo "Weeks:   " $weeks 
	sleep 1 
done 

Do not forget to make bash-countdown.sh script executable before execution:

$ chmod +x bash-countdown.sh

Exectute:

./bash-countdown.sh -d 22:34

Output:

Fri Jun 11 20:55:19 EST 2010
----------------------------
Seconds:  40
Minutes:  38
Hours:    1
Days:     0
Weeks:    0

Here are simple steps on how to send an email using telnet. This a great way to test your mail server configuration such as exim, sendmail or postfix without a need for a email client. First telnet to yor mail server:

$ telnet mail.mymailserver.com 25

Use HELO command to tell mail server from which domain you are coming from:

HELO linuxconfig.org

Now we need to state from which address this email will be sent. This is done with MAIL FROM: command:

MAIL FROM: someaddress@linuxconfig.org

Next step is to specify recipient with RCPT TO:

RCPT TO: some@email.add

Now we ca star writing some subject and body. To do that we need to use DATA command. First type DATA followed by Subject: and body. Once done enter . to send email to be queued.

DATA
Subject: Sending an email using telnet

Hello,

Here is my body? Do you like it?

cheers
.

Do not forget "." at the end of the message. To quit type

quit