Hi I am suspecting that Apache is eating up a lot of my memory, here are the first few entries of ps:

%MEM %CPU RSS VSZ COMMAND
9.2 0.5 46952 102668 /usr/sbin/apache2 -k start
8.8 0.4 45208 101556 /usr/sbin/apache2 -k start
8.7 0.4 44752 101636 /usr/sbin/apache2 -k start
6.2 0.3 31936 87640 /usr/sbin/apache2 -k start
6.2 0.2 31996 87840 /usr/sbin/apache2 -k start
4.7 0.0 24084 77840 /usr/sbin/apache2 -k start
2.8 0.2 14352 133116 /usr/sbin/mysqld
2.1 0.0 10932 15288 /usr/bin/perl /usr/share/webmin/miniserv.pl /etc/webmin/miniserv.conf
1.9 0.0 9812 14056 /usr/bin/perl /usr/share/usermin/miniserv.pl /etc/usermin/miniserv.conf
1.2 0.0 6136 10888 /usr/bin/python /var/lib/mailman/bin/qrunner --runner=OutgoingRunner:0:1 -s
1.1 0.0 6096 10912 /usr/bin/python /var/lib/mailman/bin/qrunner --runner=BounceRunner:0:1 -s
1.1 0.0 6084 10860 /usr/bin/python /var/lib/mailman/bin/qrunner --runner=NewsRunner:0:1 -s
1.1 0.0 6048 10864 /usr/bin/python /var/lib/mailman/bin/qrunner --runner=CommandRunner:0:1 -s
1.1 0.0 6040 10800 /usr/bin/python /var/lib/mailman/bin/qrunner --runner=VirginRunner:0:1 -s
1.1 0.0 6036 10884 /usr/bin/python /var/lib/mailman/bin/qrunner --runner=IncomingRunner:0:1 -s
1.1 0.0 6036 10800 /usr/bin/python /var/lib/mailman/bin/qrunner --runner=RetryRunner:0:1 -s
1.1 0.0 6032 10888 /usr/bin/python /var/lib/mailman/bin/qrunner --runner=ArchRunner:0:1 -s
10.2 0.5 51980 108792 /usr/sbin/apache2 -k start

Can anyone suggest what I should do to optimise apache mem usage?

Run

ps aux --sort -rss

to give a sorted list of processes by memory usage.

What size is your linode? What's your apache max clients value? You should also disable any apache modules you don't use.

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Result (first few lines):

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
www-data  6020  0.4 11.9 115880 61060 ?        S    04:07   0:08 /usr/sbin/apach
www-data  9901  0.7 11.4 112800 58436 ?        S    04:34   0:03 /usr/sbin/apach
www-data  9909  0.5  9.6 104512 48920 ?        S    04:34   0:02 /usr/sbin/apach
www-data  9910  0.7  9.1 102020 46860 ?        S    04:34   0:03 /usr/sbin/apach
www-data 10605  0.4  8.8 100448 45188 ?        S    04:37   0:01 /usr/sbin/apach
www-data  9908  0.6  5.6  84684 28652 ?        S    04:34   0:03 /usr/sbin/apach
root      3513  0.0  4.1  77840 20996 ?        Ss   03:51   0:00 /usr/sbin/apach
mysql     2124  0.2  2.2 132272 11332 ?        Ssl  03:50   0:06 /usr/sbin/mysql
root      3558  0.0  2.1  15288 10916 ?        Ss   03:51   0:00 /usr/bin/perl /
root      3554  0.0  1.9  14056  9804 ?        Ss   03:51   0:00 /usr/bin/perl /
root      3250  0.0  0.8  58492  4092 ?        Ss   03:50   0:00 /usr/bin/php5-f
www-data  3252  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3253  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3254  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3255  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3257  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3258  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3259  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3260  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3261  0.0  0.6  58492  3332 ?        S    03:50   0:00 /usr/bin/php5-f
www-data  3251  0.0  0.6  58492  3328 ?        S    03:50   0:00 /usr/bin/php5-f

Size of my linode is 512mb

Max clients value is 24.

How can I know which modules are running and which I can disable?

Thanks

Are you running php-fpm with apache prefork?

To check your apache modules run

apache2ctl -M

or

httpd -M

depending on your distribution.

If you see prefork in the output you're using apache prefork.

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Prefork:

Loaded Modules:
 core_module (static)
 log_config_module (static)
 logio_module (static)
 mpm_prefork_module (static)
 http_module (static)
 so_module (static)
 actions_module (shared)
 alias_module (shared)
 auth_basic_module (shared)
 auth_digest_module (shared)
 authn_file_module (shared)
 authz_default_module (shared)
 authz_groupfile_module (shared)
 authz_host_module (shared)
 authz_user_module (shared)
 autoindex_module (shared)
 cgi_module (shared)
 dav_module (shared)
 dav_fs_module (shared)
 dav_svn_module (shared)
 authz_svn_module (shared)
 deflate_module (shared)
 dir_module (shared)
 env_module (shared)
 fcgid_module (shared)
 ldap_userdir_module (shared)
 mime_module (shared)
 negotiation_module (shared)
 php5_module (shared)
 proxy_module (shared)
 proxy_balancer_module (shared)
 proxy_connect_module (shared)
 proxy_http_module (shared)
 reqtimeout_module (shared)
 rewrite_module (shared)
 ruby_module (shared)
 setenvif_module (shared)
 ssl_module (shared)
 status_module (shared)
 suexec_module (shared)
Syntax OK

You have php processes running and a php module in apache, find out which you're using and remove the one you're not.

Unless you're using svn or web dav you can disable the following modules
dav_module (shared)
dav_fs_module (shared)
dav_svn_module (shared)
authz_svn_module (shared)

these are for proxies if you don't use them disable them
proxy_module (shared)
proxy_balancer_module (shared)
proxy_connect_module (shared)
proxy_http_module (shared)

You an disable a module with a2dismod <modulename>

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ok that seems to have been successful in freeing up memory. Is there anything else I should do as regards to optimisation?

Using mod_expires to set browser cache times for static content (i.e. images) is a good idea it saves requests to your server, also enabling mod_deflate to gzip content will speed up page loads for your users.

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Thanks

I am still getting out of memory errors, logging to Lish I can see such problems:

Killed process 17360 (apache2) total-vm:239140kB, anon-rss:90524kB, file-rss:11084kB
Out of memory: Kill process 20387 (apache2) score 174 or sacrifice child
Killed process 20387 (apache2) total-vm:195052kB, anon-rss:80256kB, file-rss:11188kB
Out of memory: Kill process 27927 (apache2) score 193 or sacrifice child
Killed process 27927 (apache2) total-vm:210392kB, anon-rss:71720kB, file-rss:10584kB
Out of memory: Kill process 31105 (apache2) score 314 or sacrifice child
Killed process 31105 (apache2) total-vm:301676kB, anon-rss:96544kB, file-rss:11056kB
Out of memory: Kill process 11698 (apache2) score 194 or sacrifice child
Killed process 11698 (apache2) total-vm:209428kB, anon-rss:57528kB, file-rss:10912kB
Out of memory: Kill process 15455 (apache2) score 178 or sacrifice child
Killed process 15455 (apache2) total-vm:197244kB, anon-rss:67324kB, file-rss:11088kB
Out of memory: Kill process 16286 (apache2) score 170 or sacrifice child
Killed process 16286 (apache2) total-vm:191056kB, anon-rss:81816kB, file-rss:11172kB
Out of memory: Kill process 20750 (apache2) score 176 or sacrifice child
Killed process 20750 (apache2) total-vm:196980kB, anon-rss:51100kB, file-rss:11104kB
Out of memory: Kill process 23842 (apache2) score 106 or sacrifice child
Killed process 23842 (apache2) total-vm:140764kB, anon-rss:36784kB, file-rss:11060kB
Out of memory: Kill process 26947 (apache2) score 177 or sacrifice child
Killed process 26947 (apache2) total-vm:201232kB, anon-rss:85516kB, file-rss:5608kB
Out of memory: Kill process 27700 (apache2) score 198 or sacrifice child
Killed process 27700 (apache2) total-vm:213572kB, anon-rss:87204kB, file-rss:10200kB
Out of memory: Kill process 27690 (apache2) score 189 or sacrifice child
Killed process 27690 (apache2) total-vm:206240kB, anon-rss:85276kB, file-rss:9892kB
Out of memory: Kill process 28459 (apache2) score 184 or sacrifice child
Killed process 28459 (apache2) total-vm:204356kB, anon-rss:27720kB, file-rss:10200kB
Out of memory: Kill process 3762 (apache2) score 72 or sacrifice child
Killed process 3762 (apache2) total-vm:117180kB, anon-rss:31216kB, file-rss:8224kB
Out of memory: Kill process 2868 (apache2) score 64 or sacrifice child
Killed process 2868 (apache2) total-vm:116804kB, anon-rss:16088kB, file-rss:3128kB
Out of memory: Kill process 2124 (mysqld) score 49 or sacrifice child
Killed process 2124 (mysqld) total-vm:143176kB, anon-rss:13476kB, file-rss:0kB

what does ps aux --sort -rss show now? Also install munin it's a great resource tracker.

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