The Linux system log daemon is responsible for logging system messages. Starting RHEL 6, The system log daemon/service and its configuration file is rsyslogd – /etc/rsyslog.conf. The post describes how to modify CentOS / RHEL 6,7 system log message verbosity.
Verbosity level for rsyslogd
Each line in the configuration file /etc/rsyslog.conf defines a rule consisting of two whitespace-separated fields i.e. a selector (or filter) field and an action field.
– The selector field specifies a pattern of facilities and priorities.
– The action field specifies the target for messages matched by the selector i.e. a file (log), named pipe (fifo), tty (terminal), network address, etc.
facilities
| authpriv | security/authorization messages (private) |
| cron | clock daemon (crond and atd messages) |
| daemon | messages from system daemons without separate facility |
| kern | kernel messages |
| local[0-7] | reserved for local system use (see below) |
| lpr | printer messages (used by JetDirect cards) |
| messages from mail daemons | |
| news | USENET news subsystem messages |
| syslog | messages generated internally by syslogd |
| user | generic user-level messages |
| uucp | UUCP subsystem messages |
Priorities / Severities
| 0 | emerg | system is unusable |
| 1 | alert | action must be taken immediately |
| 2 | crit | critical conditions |
| 3 | err | error conditions |
| 4 | warning | warning conditions |
| 5 | notice | normal, but significant, condition |
| 6 | info | informational message |
| 7 | debug | debug-level message |
Following is a default sample of an RHEL 7 /etc/rsyslog.conf file. The first line instructs the syslog daemon (syslogd) to log everything of level info or higher (excluding mail, authpriv and cron facility message) to the /var/log/messages file.
cat /etc/rsyslog.conf *.info;mail.none;authpriv.none;cron.none /var/log/messages authpriv.* /var/log/secure mail.* -/var/log/maillog cron.* /var/log/cron *.emerg * uucp,news.crit /var/log/spooler local7.* /var/log/boot.log
Increasing default syslog message verbosity
1. To increase the default syslog message verbosity e.g. from info to debug level, change the relevant syslog configuration file entry e.g.:
from:
*.info;mail.none;authpriv.none;cron.none /var/log/messages
to:
*.debug;mail.none;authpriv.none;cron.none /var/log/messages
2. To send debug level messages (but not messages of other levels) for all facilities to virtual console 9 (/dev/tty9), add the following syslog configuration file entry:
*.=debug /dev/tty9
3. When making changes to the system log configuration file, a restart of the rsyslogd service (or system reboot) is required for changes to take effect e.g.:
For RHEL 6 :
# service rsyslogd restart
For RHEL 7 :
# systemctl restart rsyslog