After performing some security related OS updates, i was receiving from LDAP all sort of strange errors. Like, when you logged on the ldap server as a regular ldap user (not system user) the regular user@host:~$ prompt changed to:
I have no name!@host:~$
Read the rest of this entry »

According to tune2fs manual, reserved blocks are designed to keep your system from failing when you run out of space. Its reserves space for privileged processes such as daemons (like syslogd, for ex.) and other root level processes; also the reserved space can prevent the filesystem from fragmenting as it fills up. By default this is 5% regardless of the size of the partition.

On large partitions (250GB drives and up are quite common these days), the default 5% reserved space can be quite a lot (12.5Gb in my example). For ext3 partitions you can tune this parameter by using tune2fs with the parameter -m. For ex. to decrease this to 3% you would run (for ex. on /dev/sda1):
tune2fs -m3 /dev/sda1
You should be very careful when ‘playing’ with this parameter and be sure you know what you are doing before changing this value.

This document describes how to install and use sshfs, a FUSE based filesystem that uses SSH to mount remote folders. Since it is based on FUSE (userspace filesystem framework for Linux) your kernel will need to have the fuse module available. FUSE is included in kernel newer than 2.6.14, so I will assume that you will have it already included in your kernel.

Read the rest of this entry »

If you have seen an error like “Fatal Error: PHP Allowed Memory Size Exhausted” in apache logs or in your browser, this means that PHP has exhausted the maximum memory limit. This post will show 3 different ways on how you can increase the php memory limit and also explain when you should use them.

First, let’s see where is this limit coming from. Normally you will see from the error message what is the actual limit, as this will look like:
PHP Fatal error: Allowed memory size of X bytes exhausted (tried to allocate Y) in whatever.php
The default value might differ depending on what php version and linux distribution you are running, but normally this will be set to either 8M or 16M. For example on my debian etch, running on php 5.2 this is set by default at 16M.

In order to identify the current value on your system, look inside your php.ini and search for memory_limit:
memory_limit = 16M ; Maximum amount of memory a script may consume (16MB)

There are three ways to change this value, the obvious way - changing the global value from php.ini, but also an individual method to change it just for a script, or folder. Read the rest of this entry »

Normally MySQL replication will stop whenever there is an error running a query on the slave. This happens in order for us to be able to identify the problem and fix it, and keep the data consistent with the mater that has sent the query. You can skip such errors, even if this is not recommended, as long as you know really well what are those queries and why they are failing, etc.

For example you can skip just one query that is hanging the slave using:
mysql>SET GLOBAL SQL_SLAVE_SKIP_COUNTER=1; START SLAVE;

There might be cases where you will want to skip more queries. For example you might want to skip all duplicate errors you might be getting (output from show slave status;):
"1062 | Error 'Duplicate entry 'xyz' for key 1' on query. Default database: 'db'. Query: 'INSERT INTO ..."

Read the rest of this entry »

The Unix find command is a very powerful tool, and this short post is intended to show how easy you can achieve something that might look complicate: to find all the files of a particular size. Let’s assume you are searching for all the files of exactly 6579 bytes size inside the home directory. You will just have to run something like:

find /home/ -type f -size 6579c -exec ls {} \;

As units you can use:

• b - for 512-byte blocks (this is the default if no suffix is used)
• c - for bytes
• w - for two-byte words
• k - for Kilobytes (units of 1024 bytes)
• M - for Megabytes (units of 1048576 bytes)
• G - for Gigabytes (units of 1073741824 bytes)

Read the rest of this entry »

Apache is one complex piece of software, that contains many features most people are normally not using. You can do so many things with apache outside of the default configurations, and I am not going to discuss today about an external module, but about the plain old mod_log_config.

Normally most people will use for apache logging the combined LogFormat, and will not even think there will be other possible additions to that. This normally looks like:
LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined
and it contains most of the information we would like to see in the logs. Still there are many other information we can include here… just see below for the full list. Read the rest of this entry »

Here is a quick tip that will show several methods how you can install pear beta packages. Normally if you will try to install a pear package that has not released yet a stable version, you will receive an error like:

pear install Translation2
Failed to download pear/Translation2 within preferred state "stable", latest release is version 2.0.0RC3, stability "beta", use "channel://pear.php.net/Translation2-2.0.0RC3" to install
Cannot initialize 'channel://pear.php.net/Translation2', invalid or missing package file
Package "channel://pear.php.net/Translation2" is not valid
install failed
Read the rest of this entry »

Here is a quick tip that will show several methods to change the mysql root password (that is normally empty at mysql initial install).

Method 1: using the SET PASSWORD command:

mysql -u root
mysql> SET PASSWORD FOR 'root'@'localhost' = PASSWORD('newpass');

Method 2: using mysqladmin

mysqladmin -u root password "newpass"

Read the rest of this entry »

Here is a quick tip how to create from mysql cli a new database and a new mysql user that has full privileges on this newly created database:
mysql -uroot -p
<enter_mysql_root_pass>
CREATE DATABASE <DB_NAME>;
GRANT ALL PRIVILEGES ON <DB_NAME>.* TO 'my_user'@'localhost' IDENTIFIED BY 'my_password' WITH GRANT OPTION;

Read the rest of this entry »