In order to setup automatic start, we will have to deal with /etc/init.d/rc.local . This is the file, that is processed on system startup and it will allow you to run anything you like. We need to start Apache using /usr/local/apache2/bin/apachectl start. Let’s add this string to the end of your /etc/init.d/rc.local

#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don’t
# want to do the full Sys V style init stuff.

touch /var/lock/subsys/local
/usr/local/apache2/bin/apachectl start

That’s all! Now your httpd daemon will be automatically started at boot. You can start any daemon this way. If you know any more methods to start daemons, please, add them in comments.

find /path/to/folder/* -mtime +7 -exec rm {} \;

Please, note, that you need to keep spaces between command arguments.

This command is suitable for folders that contain a large number of files. In order to force file deletion you need to add -f key.

find /path/to/folder/* -mtime +7 -exec rm {} \;

If you need to move these files instead of deletion, here is the solution:

find /path/to/folder/* -mtime +7 -exec mv {} /path/test-mv-to/ \;

Hope this helps you to deal with archive files and big folders.

kill `ps aux | grep php_script.php | grep -v grep | awk '{print $2}'`

What does this command actually do? It sends process IDs found by ps to the kill command. Then all these processes are killed. This command is used when any other methods, like killall -9 php are not acceptable for any reason.

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The most common use of the sticky bit today is related to directories. When the sticky bit is set, only the item’s owner, the directory’s owner, or the root can rename, delete, or modify files. Without the sticky bit set, any user with write and execute permissions for the directory can rename or delete contained files, regardless of owner. Typically this is set on the /tmp directory to prevent users from deleting or moving other users’ files.

In order to set the sticky bit, a simple command is used:

chmod +t /tmp


In order to check whether the sticky bit is set, here is another command:

ls -ld /tmp

If you r last bit is ‘t’, then the sticky bit is set to the directory. It is a common practice to protect this folder in such a way as many server applications store their temporary data in this directory. For example, default MySQL configuration is set to store its socket file in /tmp/mysql.sock. You can experience problems if you don’t set a sticky bit on your /tmp directory.

When you need to establish connection with a hostname, that has a dynamic IP address (most typical situation – a hostname, that has an unstable Internet connection), Dynamic DNS becomes a simple yet stable solution.

When a hostname obtains an IP address, it is automatically sent to Dynamic DNS system, but users are able to connect using a symbolic name, that remains unchanged (for example, hostname.com).  In order to prevent IP caching, Dynamic DNS records have low TTL values (e.g. 60 seconds).

We’re going to cover the process of using such a configuration with a pppd connection, this package is widely used in Linux with almost all types of Internet connections.

We will take dyndns.org as a Dynamic DNS provider (you’re welcome to select another one: there is no real difference between them). We won’t describe the process of signing up and creating DNS records, but you’re always welcome to follow this guide, and ask us if anything is unclear, though it should be.

We will use inadyn for our connections. It gives the possibility to have your own fixed hostname registered on the internet, although your IP might be changing. It checks periodically whether the IP address stored by the DNS server is the real current IP address of the machine that is running INADYN. Though there are some limitations, that are described here, it is a simple solution, that doesn’t require any specific knowledge. It is a free software, that allows to connect with many Dynamic DNS providers, and you can obtain it by following this link.

You will need to download it, unpack and compile using make.

We will use it in the following way:

inadyn is started when the connection is being established (pppd acquires an IP address and creates an interface). Immediately after that it tries to perform an update and then remains in memory to periodically check for updates. If inadyn is already present in memory, it will be terminated before running a new instance.

In order to do that, we need to touch /etc/ppp/ip-up.local file (create a new one if it doesn’t exist) with the following contents:

#!/bin/sh
kill `ps -A |grep inadyn |sed ‘s/[ |\t].*$//’`
sleep 1
/etc/ppp/inadyn -u login -p xxxxx -a lampdocs.dyndns.org –background –update_period_sec 3600

Replace xxxxx with your password, login with your username, obtained at dyndns.org and lampdocs.dyndns.org with a symbolic name you’ve set for your host with dynamic IP.

You can change kill `ps -A |grep inadyn |sed ‘s/[ |\t].*$//’` if you don’t like it. Here is another variant:

#!/bin/sh
pkill inadyn
sleep 1
/etc/ppp/inadyn -u login -p xxxxx -a lampdocs.dyndns.org –background –update_period_sec 3600

That’s enough for configuration. Inadyn will be automatically started when a new pppd connection is established. You might need to enable inadyn requests in firewall, so it could connect using http without any problems. Inadyn requires just 2 addresses to connect, and both of them have fixed IPs:

checkip.dyndns.org (IP 208.78.70.70)
members.dyndns.org (IP 204.13.248.112)

You can enable these requests by issuing the following commands:

iptables -t filter -I OUTPUT -p tcp -d 208.78.70.70 –destination-port 80 -j ACCEPT
iptables -t filter -I OUTPUT -p tcp -d 204.13.248.112 –destination -port 80 -j ACCEPT

Then you should input

iptables -t filter -I INPUT -p tcp -s 208.78.70.70 –source-port 80 -j ACCEPT
iptables -t filter -I INPUT -p tcp -s 204.13.248.112 –source-port 80 -j ACCEPT

Or

iptables -t filter -I INPUT -m state –state ESTABLISHED,RELATED -j ACCEPT

- they have the same functionality for our needs. That’s all, Dynamic DNS should be working for you. Note, that you will have to configure inadyn if you choose another Dynamic DNS provider, the configuration is not complicated and you can find it in inadyn documentation.

Please, let us know if you have any problems using Dynamic DNS.

First of all, we will need to download and install GeoIP. We will take free version, but if you really require good stats, you may buy one. Let’s switch to a temporary directory to issue the following commands:

wget http://maxmind.com/download/geoip/api/c/GeoIP.tar.gz;
tar xzvf GeoIP.tar.gz;
cd GeoIP-1.4.6;
./configure;
make;
make install;

You might need to replace 1.4.6 with your version of Geoip, as 1.4.6 is the latest one for today.

Then we need to install Geoip using cpan. I suppose, that you are already familiar with cpan, that’s why I won’t describe initial span setup procedure here. In order to install it, we need to enter cpan from command line. Then issue the following command:

install Geo::IP

Then type quit. And the final stage: we will add Geoip support to awstats.conf. You’re welcome to do it with any editor you like, here is a command line variant using sed.

sed -i ‘s/#LoadPlugin=”geoip GEOIP_STANDARD \/pathto\/GeoIP.dat”/LoadPlugin=”geoip GEOIP_STANDARD \/usr\/local\/share\/GeoIP\/GeoIP.dat”/’ /etc/awstats/*.conf

You’re done now. Have fun with your updated awstats!

How do those files usually look like? For example, there was archive.rar before. When it is splitted into 3 parts, we will have archive.rar.000, archive.rar.001, archive.rar.002. How do we join them together?

There is a simple command line solution for this:

cat archive.rar.* > archive.rar

This will join all the parts to a single rar file. Then you fill be able to unrar it. No matter, what was the file type, this is the easiest way to join files together, if they were splitted before.

Let’s determine when we need to have this file on our machine.When we’re compiling any “old” package from sources, we may receive the following error:

error: stropts.h: No such file or directory

What could be the reason and why isn’t this file included into our Linux distribution?This error means that your system doesn’t support STREAMS.

Linux doesn’t support STREAMS (many years ago it was available as a third party module, but it hasn’t worked for years). stropts.h is part of a POSIX XSR option, which is not supported in modern Linux distributions. Do we really need it in Linux?

This means that software you’re trying to compile, will not use the functions listed under stropts.h as they’re not supported by the operating system. So we will do a simple trick that will let you to compile your software without these functions.

Since the stropts.h is required for a successful compilation, the most simple way to solve the issue is to create a blank file named stropts.h under /usr/include. You may want to put any comments there, this way you won’t forget what was the reason to create this file.

This simple trick will help you to compile pptp (1.7.2),  pppd (2.4.5), and I think that the list will be much bigger. That was just my experience, but the sense remains the same: you need this file for a successful compilation. Just create it and have fun!

1. Ensure you’ve got ntp installed. Run rpm -qa | grep ntp to find out if it already exists on your system and yum install ntp if it is not present.

2. Run ntpdate. On CentOS, you will probably get this error:

[root@server ~]# ntpdate
29 Jan 09:52:54 ntpdate[8463]: no servers can be used, exiting

This means you have to include a server into your request, just like shown below.

[root@server ~]# ntpdate 0.pool.ntp.org
29 Jan 10:08:07 ntpdate[8853]: step time server 213.198.55.2 offset 676.605025 sec

This means my server had a 10-minute time diffrence with the time server. After this command my time has been adjusted.

3. Add time synchronization to your crontab and run it as often as you need.

30 * * * * /usr/sbin/ntpdate -s 0.pool.ntp.org

Will sync your clock every hour; I think is enough to perform synchronization weekly.  Let’s do it.

30 10 5 * * /usr/sbin/ntpdate -s 0.pool.ntp.org

This simple guide will keep your clock synchronized. Have fun!

/etc/mail/local-host-names is a text file, that contains the list of domain names and it is taken by sendmail when checking outgoing mail. You should make sure you have this file in the following format:

# local-host-names sample file
lampdocs.com
test.lampdocs.com
# end of file

Please, note, that you should leave the comment on the last line as it is ignored by sendmail. Your local-host-names should have the last line either blank, either commented. Hope this saves someone some time, as this feature is not so well documented and you might have problems with the last domain in the list.