February 6, 2007 : nixCraft FAQ Roundup

in Categories FAQ last updated February 6, 2007

Recently updated/posted Linux and UNIX FAQ:

=> Shell command or script to write simple output on screen under Linux and UNIX

=> Delete a log files in Linux or UNIX

=> VSFTPD limit the number of simultaneous vsftpd connections for a single IP address

=> Gnome Desktop Keyboard Shortcut Keys

=> Disable Advanced power management (APM) on Linux

=> Locate files on linux, FreeBSD and UNIX system

=> List installed packages on Linux or FreeBSD / OpenBSD system

=> Howto: Use mysql or run mysql queries from shell script

=> Linux configure batch jobs using at command

=> Solaris add a new swap file for database

=> Apache server view performance status with mod_status configuration

=> Howto Secure portmap service using iptables and TCP Wrappers under Linux

Shell script to check / monitor domain renew / expiration date

in Categories Linux, Shell scripting, Suse Linux, Sys admin, Tips, Ubuntu Linux, UNIX last updated January 24, 2007

Update: Check out new improved domain-check script.

Forgetting to renew your domain name can happen to all of us. According to this post:
Reports are coming in from Germany that Google.de was down for many hours yesterday, and has now gone live again. We’re trying to confirm the reason, but it appears to be because Google forgot to renew the Google.de domain name..

I am going to share my little (read as dirty) shell script. It monitors and lists domain expiration date.

whois command line client for the whois directory service. It provides domain whois information. To find out nixcraft.com domain information you need to type:
$ whois nixcraft.com

Find domain expiration date

To get expiration date use grep command:
$ whois nixcraft.com | egrep -i 'Expiration|Expires on'

 Expiration Date: 10-may-2009
NOTICE: The expiration date displayed in this record is the date the
currently set to expire. This date does not necessarily reflect the expiration
view the registrar's reported date of expiration for this registration.
      Expires on: 10-May-09

Here is my script:

# Domain name list - add your domainname here
DOM="theos.in cricketnow.in nixcraft.com nixcraft.org nixcraft.biz nixcraft.net nixcraft.info cyberciti.biz cyberciti.org gite.in nixcraft.in"
for d in $DOM
  echo -n "$d - "
  whois $d | egrep -i 'Expiration|Expires on' | head -1
  # If you need list..
  # whois $d | egrep -i 'Expiration|Expires on' | head -1 >> /tmp/domain.date
  echo ""
# [ -f /tmp/domain.date ] && mail -s 'Domain renew / expiration date' you@yahoo.com < /tmp/domain.date || :


theos.in - Expiration Date:28-Oct-2007 13:01:58 UTC

cricketnow.in - Expiration Date:29-Jul-2008 09:17:56 UTC

nixcraft.com -    Expiration Date: 10-may-2009

nixcraft.org - Expiration Date:13-Aug-2007 14:58:30 UTC

nixcraft.biz - Domain Expiration Date:                      Fri Jun 01 23:59:59 GMT 2007

nixcraft.net -    Expiration Date: 11-dec-2007

nixcraft.info - Expiration Date:26-Jun-2007 11:05:13 UTC

cyberciti.biz - Domain Expiration Date:                      Tue Jun 30 23:59:59 GMT 2009

cyberciti.org - Expiration Date:25-May-2007 11:20:40 UTC

gite.in - Expiration Date:14-Sep-2007 06:47:36 UTC

nixcraft.in - Expiration Date:02-Feb-2008 05:33:08 UTC

Install a script and run on weekly / monthly basis via Linux/UNIX Cron facility.

HowTo: Backup MySQL Databases, Web server Files to a FTP Server Automatically

in Categories Data recovery, Linux, MySQL, Shell scripting last updated August 10, 2006

This is a simple backup solution for people who run their own web server and MySQL database server on a dedicated or VPS server. Most dedicated hosting provider provides backup service using NAS or FTP servers. These service providers will hook you to their redundant centralized storage array over private VLAN. Since, I manage couple of boxes, here is my own automated solution. If you just want a shell script, go here (you just need to provided appropriate input and it will generate FTP backup script for you on fly, you can also grab my php script generator code).

Change Linux or UNIX system password using PHP script

in Categories Apache, lighttpd, php, Shell scripting last updated August 3, 2006

If you just wanted to change your own password or other user passwords use passwd command.

I was asked to setup a PHP based interface to change the password. Since my knowledge of php is limited. Here is what I did:

Warning: This is an outdated and insecure information. Please see the official php.net document for more information. You have been warned to ignore this post.

Required tools/setup:

You must have following tools/software installed

=> Shell script to change password

=> Sudo access

=> Apache or Lighttpd web server

=> PHP server side

Step # 1: Setup a shell script to change password

This shell script use expect tool to change the password (see more about expect tool here).

Sample shell script code

# \
exec expect -f "$0" ${1+"$@"}
set password [lindex $argv 1]
spawn passwd [lindex $argv 0]
sleep 1
expect "assword:"
send "$password\r"
expect "assword:"
send "$password\r"
expect eof

You can execute this script as follows (dowload link):
$ chpasswd username password

Download script and copy to your webroot or location where webserver can read this script file:
$ cp chpasswd /var/www/

ALTERNATIVELY, if you are using Ligtttpd web server:
$ cp chpasswd /home/lighttpd

Step # 2: Setup sudo to execute a command as root user

Apache or Lighttpd web server drops root privileges as soon as they go into background. This makes changing password scenario difficult as passwd command needs root privileges to change other user account password.

Typically, Apache 2 use www-data user and Lighttpd use lighttppd username to drop privileges. Login as root user and type the following command:
# visudo

Now allow your web server to execute a script (chpasswd) w/o password. If you are using Apache web server, type the following command:
www-data ALL=NOPASSWD: /var/www/chpasswd

ALTERNATIVELY, if you are using Ligtttpd web server, type the following command:
lighttpd ALL=NOPASSWD: /home/lighttpd/chpasswd

Save and close the file.

Step # 3: Create a PHP based interface

Now you need to write a php script. Here is sample php script. This is a demo script. You should modify it according to your requirement or setup. At minimum, you need to setup correct shell script location so that it will work for you out of box. Open php script and locate line:
$shellscript = "sudo /home/lighttpd/chpasswd";

Change it to point to correct location. PHP Source code:

// change .. me! - shell script name
$shellscript = "sudo /home/lighttpd/chpasswd";
// Make sure form is submitted by user
if(!(isset($_POST['pwdchange']))) {
 // if not display them form
 writeHead("Change password");
else {
 // try to change the password
 // get username and password
 $_POST['username'] = stripslashes(trim($_POST['username']));
 $_POST['passwd'] = stripslashes(trim($_POST['passwd']));
// if user skip our javascript ...
// make sure we can only change password if we have both username and password
 if(empty($_POST['username'])) {
 if(empty($_POST['passwd'])) {
 if ( $callshell == true ) {
  // command to change password
  $cmd="$shellscript " . $_POST['username'] . " " . $_POST['passwd'];
  // call command
  // $cmd - command, $output - output of $cmd, $status - useful to find if command failed or not
   if ( $status == 0 ) { // Success - password changed
   writeHead("Password changed");
   echo '<h3>Password changed</h3>Setup a new password';
   else { // Password failed
      writeHead("Password change failed");
      echo '<h3>Password change failed</h3>';
      echo '<p>System returned following information:</p>';
      echo '<p><em>Please contact tech-support for more info! Or try <a href='.$_SERVER['PHP_SELF'].'again</a></em></p>';
 else {
   writeHead("Something was wrong -- Please try again");
   echo 'Error - Please enter username and password';
// display html head
function writeHead($title) {
echo '
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<title> ' .$title. '</title>
<style type="text/css" media="screen">
.passwdform {
	position: static;
	overflow: hidden;
.passwdleft {
	width: 25%;
	text-align: right;
	clear: both;
	float: left;
	display: inline;
	padding: 4px;
	margin: 5px 0;
.passwdright {
	width: 70%;
	text-align: left;
	float: right;
	display: inline;
	padding: 4px;
	margin: 5px 0;
.passwderror {
	border: 1px solid #ff0000;
.passwdsubmit {
// display html form
function writeForm() {
echo '
<h3>Use following form to change password:</h3>
function checkForm() {
if (document.forms.changepassword.elements[\'username\'].value.length == 0) {
    alert(\'Please enter a value for the "User name" field\');
    return false;
if (document.forms.changepassword.elements[\'passwd\'].value.length == 0) {
    alert(\'Please enter a value for the "Password" field\');
    return false;
  return true;
<div class="contactform">
<form action="' . $_SERVER[PHP_SELF]. '" method="post" onSubmit="return checkForm()" name="changepassword">
<div class="passwdleft"><label for="lblusername">User Name: </label></div>
<div class="passwdright"><input type="text" name="username" id="lblusername" size="30" maxlength="50" value="" /> (required)</div>
<div class="passwdleft"><label for="lblpasswd">Password: </label></div>
<div class="passwdright"><input type="password" name="passwd" id="lblpasswd" size="30" maxlength="50" value="" /> (required)</div>
<div class="passwdright"><input type="submit" name="Submit" value="Change password" id="passwdsubmit" />
<input type="hidden" name="pwdchange" value="process" /></div>
// display footer
function writeFoot(){
echo '</body>

Step # 4: Run the script

Point a web browser to your server url – https://mydomain.com/changepassword.php. You should see a username and password form as follows:

changepassword php script output # 1

If a password is changed successfully, you should get confirmation as follows:

changepassword php script output # 2

For some reason if a password failed to change, you should get detailed error message as follows:

changepassword php script output # 3

Step # 5: Security

Note this is an example and not final solution as it is little insecure.

  • Never ever run this script over http session. Always run over https session.
  • Put script in a password protected directory (see how to setup Apache or Lighttpd web server password protected directory).
  • Never ever, trust user input. Above php script is just a sample, for real life production you should consider more powerful user input validation. Discussion regarding PHP programming security is beyond the scope of this article. You can consult a good PHP book or search a web using your favorite search engine 🙂

Shell script to watch the disk space

in Categories Howto, Linux, Monitoring, Shell scripting last updated July 13, 2006

df displays the amount of disk space available on the file system containing each file name argument. If no file name is given, the space available on all currently mounted file systems is shown. Read man page of df if you are new to df command.


=> Find disk space using df

=> Filter out filesystem and find out the percentage of space using grep

=> Write a shell script

Step # 1: First get disk space:

$ df -H


Filesystem             Size   Used  Avail Use% Mounted on
/dev/hdb1               20G    14G   5.5G  71% /
tmpfs                  394M   4.1k   394M   1% /dev/shm
/dev/hdb5               29G    27G   654M  98% /nas/www

Step # 2: Next filter out filesystem and find out the percentage of space

$ df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }'


71% /dev/hdb1
98% /dev/hdb5

Step # 3: Write a shell script

Above command displays field 5 and 1 of df command. Now all you need to do is write a script to see if the percentage of space is >= 90% (download script):

df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output;
  echo $output
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
  partition=$(echo $output | awk '{ print $2 }' )
  if [ $usep -ge 90 ]; then
    echo "Running out of space \"$partition ($usep%)\" on $(hostname) as on $(date)" |
     mail -s "Alert: Almost out of disk space $usep%" you@somewhere.com

Setup Cron job

Save and install script as cronjob. Copy script to /etc/cron.daily/ (script downolad link)
# cp diskAlert /etc/cron.daily/
# chmod +x /etc/cron.daily/diskAlert

OR install as cronjob:
crontab -e

Write cronjob as per your requirement
10 0 * * * /path/to/diskAlert

Updated script version

Tony contributed and updated my script – You can exclude selected filesystem in case you don’t want monitor all filesystems.

# set -x
# Shell script to monitor or watch the disk space
# It will send an email to $ADMIN, if the (free available) percentage of space is >= 90%.
# -------------------------------------------------------------------------
# Set admin email so that you can get email.
# set alert level 90% is default
# Exclude list of unwanted monitoring, if several partions then use "|" to separate the partitions.
# An example: EXCLUDE_LIST="/dev/hdd1|/dev/hdc5"
function main_prog() {
while read output;
#echo $output
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1)
  partition=$(echo $output | awk '{print $2}')
  if [ $usep -ge $ALERT ] ; then
     echo "Running out of space \"$partition ($usep%)\" on server $(hostname), $(date)" | \
     mail -s "Alert: Almost out of disk space $usep%" $ADMIN

if [ "$EXCLUDE_LIST" != "" ] ; then
  df -H | grep -vE "^Filesystem|tmpfs|cdrom|${EXCLUDE_LIST}" | awk '{print $5 " " $6}' | main_prog
  df -H | grep -vE "^Filesystem|tmpfs|cdrom" | awk '{print $5 " " $6}' | main_prog

How To Monitor Linux / BSD System Over Time Without Scrolling Output Using watch Command

in Categories Linux, UNIX last updated June 25, 2017

YYou can use the watch command to execute a program or shell script periodically, display its output on screen repeatedly. That allows you to look at the program output change over time. By default, the program runs every 2 seconds. Aforementioned is useful to monitor memory utilization, RAID rebuilds progress or disk space usage over time without having to look at scrolling output.