The eaccelerator installation in directadmin is easy . This procedure is same in all php linux distribution. You may need to do the following procedure. This is based on redhat / centos distributions

1) Download the latest eaccelerator source files from  http://sourceforge.net/projects/eaccelerator/   and extract it  after that run the following commands

# yum -y install autoconf
# phpize
# ./configure
# make
# make install

2) Find the php.ini using the command ” php –ini” and edit it .  The update the  “extension_dir ” current extension  directory . This path contains all the  php  third party installations.

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# php --ini | grep Configuration
Configuration File (php.ini) Path: /usr/local/etc/php5/cgi
Loaded Configuration File:         /usr/local/etc/php5/cgi/php.ini
# grep extension_dir /usr/local/etc/php5/cgi/php.ini
extension_dir = "/usr/local/lib/php/extensions/no-debug-non-zts-20090626"
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Please note the extension_dir path will be different in your server.

3) Now add the following lines at the end of php.ini

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extension="eaccelerator.so"
eaccelerator.shm_size="16"
eaccelerator.cache_dir="/var/cache/eaccelerator"
eaccelerator.enable="1"
eaccelerator.optimizer="1"
eaccelerator.check_mtime="1"
eaccelerator.debug="0"
eaccelerator.filter=""
eaccelerator.shm_max="0"
eaccelerator.shm_ttl="0"
eaccelerator.shm_prune_period="0"
eaccelerator.shm_only="0"
eaccelerator.compress="1"
eaccelerator.compress_level="9"
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4) Now create the cache folder  /var/cache/eaccelerator

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# mkdir /var/cache/eaccelerator
# chmod  777 /var/cache/eaccelerator
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5) Restart apache  and test it