**Quick note**: apache 2.4 - Max Clients is now named MaxRequestWorkers
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You can find the apache values in:
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/etc/httpd/conf/httpd.conf
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OR
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/etc/httpd/conf.modules.d/00-mpm.conf
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If no value has been set then chances are the default of 256 is set.  (Tip: run apache2buddy to find out the value if you are having trouble working it out)
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=== CentOS ===
Best command to find the current apache processes is:
<sxh bash>
pstree | grep httpd
</sxh>
Alternative: 
<sxh bash>
ps afx | grep httpd | wc
</sxh>
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What is the number of max connection the server has been configured for?
<sxh bash>
grep -i maxclients /etc/httpd/conf/httpd.conf
</sxh>
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When did apache hit max clients?
==Centos==
<sxh bash>
grep -i maxclients /var/log/httpd/error_log
</sxh>
Has it happened before? zgrep checks through ALL of the compresses and uncompressed logs, the * at the end of error represents all of the logrotated files:
<sxh bash>
zgrep -i maxclients /var/log/httpd/error_log*
</sxh>
What are the currently configured max connections?
<sxh bash>
grep -i maxc /etc/httpd/conf/httpd.conf | head -3
</sxh>
Ubuntu could have max clients configured in a number of different places, first place to look is:
<sxh bash>
grep -i maxc /etc/apache2/apache2.conf | head -4
</sxh>
or
<sxh bash>
grep -i maxc /etc/apache2/mods-enabled/mpm_prefork.conf
</sxh>
Current connections:
<sxh bash>
pstree | grep httpd
</sxh>
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== Ubuntu ==
<sxh bash>
grep -i maxclients /var/log/apache2/error_log
</sxh>
Has it happened before?
<sxh bash>
zgrep -i maxclients /var/log/apache2/error_log*
</sxh>
Current connections:
<sxh bash>
pstree | grep apache
</sxh>
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==== CentOS====


<sxh bash>
ps -H h -ylC httpd | perl -lane '$s+=$F[7];$i++;END{printf"Avg=%.1fMB\n",$s/$i/1024}'
</sxh>


==== Ubuntu ====
<sxh bash>
ps -H h -ylC apache2 | perl -lane '$s+=$F[7];$i++;END{printf"Avg=%.1fMB\n",$s/$i/1024}'
</sxh>