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we have a few virtual machines we're using as a plesk hosting servers.

one of them exhibits the following bad behaviour:

  1. apache process count goes sky-high (ive limited MaxClients to 80 to try to deal with this)
  2. server load goes sky-high as result
  3. restarting apache instantly fixes the load and apache continues to happily serve content as usual, until a few hours later when this behaviour repeats.

ive looked through all apache logs and mysql logs and /var/log/messages and dmesg, even while the spike is happening, and cant see anything unusual.

i even visited all the dynamic content pages which were served around the same time, and could not reproduce the result.

i dont know what to do :(

attached are httpd.conf (all comments removed, exactly as plesk created it*), mysql.conf, and four graphs from zabbix showing 1 day of cached memory, cpu iowait, free swap space, and 'web server active'.

does anyone have any suggestions?

*- i enabled KeepAlive to help with this problem, and set the limits myself.

my reputation is below 10 so i cant post images, nor more than one direct hyperlink

cached memory graph:

cpu iowait graph:

free swap space graph:

web server active (true or false) graph:


ServerTokens OS

ServerRoot "/etc/httpd"

PidFile run/

Timeout 120

KeepAlive On
MaxKeepAliveRequests 100
KeepAliveTimeout 5

<IfModule prefork.c>
StartServers       8
MinSpareServers    5
MaxSpareServers   20
ServerLimit      80
MaxClients       80
MaxRequestsPerChild  4000

<IfModule worker.c>
StartServers         2
MaxClients         80
MinSpareThreads     25
MaxSpareThreads     75 
ThreadsPerChild     25
MaxRequestsPerChild  0

Listen 80

LoadModule auth_basic_module modules/
LoadModule auth_digest_module modules/
LoadModule authn_file_module modules/
LoadModule authn_alias_module modules/
LoadModule authn_anon_module modules/
LoadModule authn_dbm_module modules/
LoadModule authn_default_module modules/
LoadModule authz_host_module modules/
LoadModule authz_user_module modules/
LoadModule authz_owner_module modules/
LoadModule authz_groupfile_module modules/
LoadModule authz_dbm_module modules/
LoadModule authz_default_module modules/
LoadModule ldap_module modules/
LoadModule authnz_ldap_module modules/
LoadModule include_module modules/
LoadModule log_config_module modules/
LoadModule logio_module modules/
LoadModule env_module modules/
LoadModule ext_filter_module modules/
LoadModule mime_magic_module modules/
LoadModule expires_module modules/
LoadModule deflate_module modules/
LoadModule headers_module modules/
LoadModule usertrack_module modules/
LoadModule setenvif_module modules/
LoadModule mime_module modules/
LoadModule dav_module modules/
LoadModule status_module modules/
LoadModule autoindex_module modules/
LoadModule info_module modules/
LoadModule dav_fs_module modules/
LoadModule vhost_alias_module modules/
LoadModule negotiation_module modules/
LoadModule dir_module modules/
LoadModule actions_module modules/
LoadModule speling_module modules/
LoadModule userdir_module modules/
LoadModule alias_module modules/
LoadModule rewrite_module modules/
LoadModule proxy_module modules/
LoadModule proxy_balancer_module modules/
LoadModule proxy_ftp_module modules/
LoadModule proxy_http_module modules/
LoadModule proxy_connect_module modules/
LoadModule cache_module modules/
LoadModule suexec_module modules/
LoadModule disk_cache_module modules/
LoadModule file_cache_module modules/
LoadModule mem_cache_module modules/
LoadModule cgi_module modules/
LoadModule version_module modules/
LoadModule ssl_module /usr/lib64/httpd/modules/

Include conf.d/*.conf

User apache
Group apache

ServerAdmin root@localhost

UseCanonicalName Off

DocumentRoot "/var/www/html"

<Directory />
    Options FollowSymLinks
    AllowOverride None

<Directory "/var/www/html">
    Options Indexes FollowSymLinks
    AllowOverride None
    Order allow,deny
    Allow from all

<IfModule mod_userdir.c>
    UserDir disable

DirectoryIndex index.html index.html.var index.shtml index.cfm index.php index.htm

AccessFileName .htaccess
<Files ~ "^\.ht">
    Order allow,deny
    Deny from all

TypesConfig /etc/mime.types
DefaultType text/plain
<IfModule mod_mime_magic.c>
    MIMEMagicFile conf/magic

HostnameLookups Off

ErrorLog logs/error_log

LogLevel warn

LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined
LogFormat "%h %l %u %t \"%r\" %>s %b" common
LogFormat "%{Referer}i -> %U" referer
LogFormat "%{User-agent}i" agent

CustomLog logs/access_log combined

ServerSignature On

Alias /icons/ "/var/www/icons/"
<Directory "/var/www/icons">
    Options Indexes MultiViews
    AllowOverride None
    Order allow,deny
    Allow from all

<IfModule mod_dav_fs.c>
    DAVLockDB /var/lib/dav/lockdb

ScriptAlias /cgi-bin/ "/var/www/cgi-bin/"
<Directory "/var/www/cgi-bin">
    AllowOverride None
    Options None
    Order allow,deny
    Allow from all

IndexOptions FancyIndexing VersionSort NameWidth=* HTMLTable

AddIconByEncoding (CMP,/icons/compressed.gif) x-compress x-gzip

AddIconByType (TXT,/icons/text.gif) text/*
AddIconByType (IMG,/icons/image2.gif) image/*
AddIconByType (SND,/icons/sound2.gif) audio/*
AddIconByType (VID,/icons/movie.gif) video/*

AddIcon /icons/binary.gif .bin .exe
AddIcon /icons/binhex.gif .hqx
AddIcon /icons/tar.gif .tar
AddIcon /icons/world2.gif .wrl .wrl.gz .vrml .vrm .iv
AddIcon /icons/compressed.gif .Z .z .tgz .gz .zip
AddIcon /icons/a.gif .ps .ai .eps
AddIcon /icons/layout.gif .html .shtml .htm .pdf
AddIcon /icons/text.gif .txt
AddIcon /icons/c.gif .c
AddIcon /icons/p.gif .pl .py
AddIcon /icons/f.gif .for
AddIcon /icons/dvi.gif .dvi
AddIcon /icons/uuencoded.gif .uu
AddIcon /icons/script.gif .conf .sh .shar .csh .ksh .tcl
AddIcon /icons/tex.gif .tex
AddIcon /icons/bomb.gif core

AddIcon /icons/back.gif ..
AddIcon /icons/hand.right.gif README
AddIcon /icons/folder.gif ^^DIRECTORY^^
AddIcon /icons/blank.gif ^^BLANKICON^^

DefaultIcon /icons/unknown.gif

ReadmeName README.html
HeaderName HEADER.html

IndexIgnore .??* *~ *# HEADER* README* RCS CVS *,v *,t

AddLanguage ca .ca
AddLanguage cs .cz .cs
AddLanguage da .dk
AddLanguage de .de
AddLanguage el .el
AddLanguage en .en
AddLanguage eo .eo
AddLanguage es .es
AddLanguage et .et
AddLanguage fr .fr
AddLanguage he .he
AddLanguage hr .hr
AddLanguage it .it
AddLanguage ja .ja
AddLanguage ko .ko
AddLanguage ltz .ltz
AddLanguage nl .nl
AddLanguage nn .nn
AddLanguage no .no
AddLanguage pl .po
AddLanguage pt .pt
AddLanguage pt-BR .pt-br
AddLanguage ru .ru
AddLanguage sv .sv
AddLanguage zh-CN .zh-cn
AddLanguage zh-TW .zh-tw

LanguagePriority en ca cs da de el eo es et fr he hr it ja ko ltz nl nn no pl pt pt-BR ru sv zh-CN zh-TW

ForceLanguagePriority Prefer Fallback

AddType application/x-compress .Z
AddType application/x-gzip .gz .tgz

AddHandler type-map var

AddType text/html .shtml
AddOutputFilter INCLUDES .shtml

Alias /error/ "/var/www/error/"

<IfModule mod_negotiation.c>
<IfModule mod_include.c>
    <Directory "/var/www/error">
        AllowOverride None
        Options IncludesNoExec
        AddOutputFilter Includes html
        AddHandler type-map var
        Order allow,deny
        Allow from all
        LanguagePriority en es de fr
        ForceLanguagePriority Prefer Fallback

BrowserMatch "Mozilla/2" nokeepalive
BrowserMatch "MSIE 4\.0b2;" nokeepalive downgrade-1.0 force-response-1.0
BrowserMatch "RealPlayer 4\.0" force-response-1.0
BrowserMatch "Java/1\.0" force-response-1.0
BrowserMatch "JDK/1\.0" force-response-1.0

BrowserMatch "Microsoft Data Access Internet Publishing Provider" redirect-carefully
BrowserMatch "MS FrontPage" redirect-carefully
BrowserMatch "^WebDrive" redirect-carefully
BrowserMatch "^WebDAVFS/1.[0123]" redirect-carefully
BrowserMatch "^gnome-vfs/1.0" redirect-carefully
BrowserMatch "^XML Spy" redirect-carefully
BrowserMatch "^Dreamweaver-WebDAV-SCM1" redirect-carefully

AddType application/x-httpd-php .php
AddType application/x-httpd-php-source .phps


# Default to using old password format for compatibility with mysql 3.x
# clients (those using the mysqlclient10 compatibility package).


# Disabling symbolic-links is recommended to prevent assorted security risks;
# to do so, uncomment this line:
# symbolic-links=0

share|improve this question
Where's the "apache process count spike" graph? Which webserver are you using? (prefork or threaded)? –  symcbean Nov 23 '10 at 12:38
apologies, process count spike graph: –  mykchan Nov 23 '10 at 23:24
enter button submits this comment field, great. apache is definately prefork: httpd -l Compiled in modules: core.c prefork.c http_core.c mod_so.c –  mykchan Nov 23 '10 at 23:25

2 Answers 2

Looks like it could be a memory leak. Try setting MaxRequestsPerChild to something like 100 to see if that fixes it. If so start tracing your memory leak.

It could also be a DOS attack. Do you have a spike in requests before the problems start.

share|improve this answer
up vote 2 down vote accepted

semaphores were maxed out. i dont know why apache has allocated itself ~115 semaphores but upping the value fixed all the problems - apache no longer has to IOWAIT for another semaphore, so the system doesnt hang.

echo "kernel.sem = 512 32000 100 512" >> /etc/sysctl.conf; sysctl -p; 
share|improve this answer

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