Log Locations

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Common Log Locations:

cPanel

Apache

EA3

Apache Access Logs:
  /usr/local/apache/logs/access_log

Domain access logs:
  /usr/local/apache/domlogs/<DOMAIN>

Site and service error logs:
  /usr/local/apache/logs/error_log

SuExec audit log:
  /usr/local/apache/logs/suexec_log

SuPHP audit log:
  /usr/local/apache/logs/suphp_log

EA4

Domlogs:
/var/log/apache2/domlogs/

Error log:
/var/log/apache2/error_log

suPHP Error log:
/etc/apache2/logs/suphp_log

cPanel

Service status:
  /var/log/chkservd.log

Access and user actions:
  /usr/local/cpanel/logs/access_log

Cpanel Error Logs:
  /usr/local/cpanel/logs/error_log

CSF and LFD Logs

LFD logs:
  /var/log/lfd.log

CSF Errors:
/etc/csf/csf.error

Database Logs

MySQL database logs:
/var/log/mysqld.log
/var/lib/mysql/$(HOSTNAME).err

PostgreSQL database logs:
  /var/log/pgsql

Exim

(see exim )

Fatal errors:
  /var/log/exim_paniclog

Incoming mail queue:
  /var/spool/exim/input

Exim Messages rejected based on ACLs or other policies:
  /var/log/exim_rejectlog

Exim Delivery and receipt:
  /var/log/exim_mainlog

IMAP, POP login attempts, transactions, fatal errors and spam scoring:
  /var/log/maillog
  /var/log/messages

Mailman Logs:
  /usr/local/cpanel/3rdparty/mailmain/logs

PHP-FPM

/opt/cpanel/ea-php$VERSION/root/usr/var/log/php-fpm/error.log - Logs for the Master Process/daemon

/home/$cpuser/logs/domain_tld.php.error.log - Logs for the pool/php code. What logs here? Errors specifically related to the PHP code, so PHP fatal errors, notices, deprecation warnings are all logged here, but it is reliant on PHP's error_reporting configuration, which is E_ALL & ~E_NOTICE by default.

Top sites hitting PHP-FPM limits:

grep max /opt/cpanel/ea-php*/root/usr/var/log/php-fpm/error.log | awk '{print $5}' | sort | uniq -c | sort -rn | head

System

Cron:
  /var/log/cron

Ftp Logs:
  /var/log/messages
  /var/log/xferlog (symlinked to /usr/local/apache/domlogs/ftpxferlog)

Most other logs:
  /var/log/messages

MySQL:
/var/lib/mysql/<hostname>.err
/var/log/mysqld.log

SSH Logs:
  /var/log/secure

Additional cPanel Logs

Log file location                  Description
Auto-SSL Logs                /var/cpanel/logs/autossl
Cpanel installation logs     /var/log/cpanel-install.log
Cpanel License Logs          /usr/local/cpanel/logs/license_log
Cpanel Login Logs            /usr/local/cpanel/logs/login_log
cPHulk Brute Force Logs      /usr/local/cpanel/logs/cphulkd.log
Cpanel/WHM Accounting (account creations, deletions, etc) Logs     /var/cpanel/accounting.log
Cpanel Bandwidth Logs        /var/cpanel/bandwidth/(account user name)
Cpanel/WHM Service monitor Logs     /var/log/chkservd.log
Cpanel Stats Daemon Logs     /usr/local/cpanel/logs/stats_log
Cpanel backup Logs           /usr/local/cpanel/logs/cpbackup
cPanel backup transport logs: /usr/local/cpanel/logs/cpbackup_transporter/
Update (UPCP) Log           /var/cpanel/updatelogs/update-(TIMESTAMP).log

cPanel/WHM webalizer/awstats logs     /usr/local/cpanel/logs/stats_log
cPanel/WHM version checking     /usr/local/cpanel/version

SquirrelMail     /var/cpanel/squirrelmail
RoundCube        /var/cpanel/roundcube/log
Horde            /var/cpanel/horde/log

tailwatchd log     /usr/local/cpanel/logs/tailwatch_log
EasyApache 3 Build Logs     /usr/local/cpanel/logs/easy/apache/
EA4 Update logs             /usr/local/cpanel/logs/packman/migrate_ea3_to_ea4...

Tomcat Logs         /usr/local/jakarta/tomcat/logs/catalina.err /usr/local/jakarta/tomcat/logs/catalina.out

ModSecurity Logs    /usr/local/apache/logs/modsec_audit.log /usr/local/apache/logs/modsec_debug_log

Named/Bind (DNS) logs     /var/log/messages

Plesk

Apache

Global Access and Error logs:
/var/log/httpd/

Domain logs:
/var/www/vhosts/<domain>/logs

nginx

Error log:
/var/log/nginx/error.log

Access log:
/var/log/nginx/access.log

Domain logs:
/var/www/vhosts/<domain>/logs/proxy_access*_log

Mail

Mail log:
/usr/local/psa/var/log/maillog

Plesk

Error log:
/var/log/sw-cp-server/error_log
and
/var/log/sw-cp-server/sw-engine.log

Access log:
/usr/local/psa/admin/logs/httpsd_access_log

Panel log:
/usr/local/psa/admin/logs/panel.log

Install/Upgrade logs:
/var/log/plesk/install/

Front-end logs:
/var/log/plesk/sw-cp-server/

References

Plesk documentation:
Documentation - Logs

cPanel Log Locations Poster:

cPanel Log Locations Poster