rsyslog
Related articles
rsyslog is an alternate logger to syslog-ng and offers many benefits over syslog-ng.
Contents
Installation
Starting service
You can start/enable the rsyslog service after installation.
Configure Hostname
Rsyslog uses the glibc routine gethostname()
or gethostbyname()
to determine the hostname of the local machine. The gethostname()
or gethostbyname()
routine check the contents of /etc/hosts
for the fully qualified domain name (FQDN) if you are not using BIND or NIS.
You can check what the local machine's currently configured FQDN is by running hostname --fqdn
. The output of hostname --short
will be used by rsyslog when writing log messages. If you want to have full hostnames in logs, you need to add $PreserveFQDN on
to the beginning of the file (before using any directive that write to files). This is because, rsyslog reads config file and applies it on-the-go and then reads the later lines.
The /etc/hosts
file contains a number of lines that map FQDNs to IP addresses and that map aliases to FQDNs. See the example /etc/hosts
file below:
/etc/hosts
#<ip-address> <hostname.domain.org> <hostname> #<ip-address> <actual FQDN> <aliases> 127.0.0.1 localhost.localdomain somehost.localdomain localhost somehost ::1 localhost.localdomain somehost.localdomain localhost somehost
localhost.localdomain
is the first item following the IP address, so gethostbyname()
function will return localhost.localdomain as the local machine's FQDN. Then /var/log/messages
file will use localhost as hostname.
To use somehost as the hostname. Move somehost.localdomain to the first item:
/etc/hosts
#<ip-address> <hostname.domain.org> <hostname> #<ip-address> <actual FQDN> <aliases> 127.0.0.1 somehost.localdomain localhost.localdomain localhost somehost ::1 somehost.localdomain localhost.localdomain localhost somehost
Configuration
The rsyslog doesn't create its working directory /var/spool/rsyslog
defined by the $WorkDirectory
variable in the configuration file. You might need to create it manually or change its destination.
Log output can be fine tuned in /etc/rsyslog.conf
. The daemon uses Facility levels (see below) to determine what gets put where. For example:
/etc/rsyslog.conf
# The authpriv file has restricted access. authpriv.* /var/log/secure
States that all messages falling under the authpriv facility are logged to /var/log/secure
.
Another example, which would be similar to the behaviour of syslog-ng for the old auth.log
:
/etc/rsyslog.conf
auth.* -/var/log/auth
See also
Structure of the rsyslog.conf file.
Facility Levels
Facility Number | Keyword | Facility Description |
---|---|---|
0 | kern | kernel messages |
1 | user | user-level messages |
2 | mail system | |
3 | daemon | system daemons |
4 | auth | security/authorization messages |
5 | syslog | messages generated internally by syslogd |
6 | lpr | line printer subsystem |
7 | news | network news subsystem |
8 | uucp | UUCP subsystem |
9 | clock daemon | |
10 | authpriv | security/authorization messages |
11 | ftp | FTP daemon |
12 | - | NTP subsystem |
13 | - | log audit |
14 | - | log alert |
15 | cron | clock daemon |
16 | local0 | local use 0 (local0) |
17 | local1 | local use 1 (local1) |
18 | local2 | local use 2 (local2) |
19 | local3 | local use 3 (local3) |
20 | local4 | local use 4 (local4) |
21 | local5 | local use 5 (local5) |
22 | local6 | local use 6 (local6) |
23 | local7 | local use 7 (local7) |
Security Levels
As defined in RFC 5424, there are eight security levels:
Code | Severity | Keyword | Description | General Description |
---|---|---|---|---|
0 | Emergency | emerg (panic) | System is unusable. | A "panic" condition usually affecting multiple apps/servers/sites. At this level it would usually notify all tech staff on call. |
1 | Alert | alert | Action must be taken immediately. | Should be corrected immediately, therefore notify staff who can fix the problem. An example would be the loss of a primary ISP connection. |
2 | Critical | crit | Critical conditions. | Should be corrected immediately, but indicates failure in a primary system, an example is a loss of a backup ISP connection. |
3 | Error | err (error) | Error conditions. | Non-urgent failures, these should be relayed to developers or admins; each item must be resolved within a given time. |
4 | Warning | warning (warn) | Warning conditions. | Warning messages, not an error, but indication that an error will occur if action is not taken, e.g. file system 85% full - each item must be resolved within a given time. |
5 | Notice | notice | Normal but significant condition. | Events that are unusual but not error conditions - might be summarized in an email to developers or admins to spot potential problems - no immediate action required. |
6 | Informational | info | Informational messages. | Normal operational messages - may be harvested for reporting, measuring throughput, etc. - no action required. |
7 | Debug | debug | Debug-level messages. | Info useful to developers for debugging the application, not useful during operations. |
Examples
journald with rsyslog for kernel messages
Since the syslog component of systemd, journald, does not flush its logs to disk during normal operation, these logs will be gone when the machine is shut down abnormally (power loss, kernel lock-ups, ...). In the case of kernel lock-ups, it is pretty important to have some kernel logs for debugging. Until journald gains a configuration option for flushing kernel logs, rsyslog can be used in conjunction with journald.
Summary of requirements:
- journald must still get all log messages.
- rsyslog must only log kernel messages, all other logs are handled by journald.
- Kernel logs must be logged separatedly to
/var/log/kernel.log
. - Use systemd to start the service.
Installation and configuration steps:
- Install rsyslog.
- Edit
/etc/logrotate.d/rsyslog
and add/var/log/kernel.log
to the list of logs. Without this modification, the kernel log would grow indefinitely. - Edit
/etc/rsyslog.conf
and comment everything except for$ModLoad imklog
. I also kept$ModLoad immark
to have a heart-beat logged. - Add the next line to the same configuration file:
kern.* /var/log/kernel.log;RSYSLOG_TraditionalFileFormat
- The
kern.*
part catches all messages originating from the kernel.;RSYSLOG_TraditionalFileFormat
is used here to use a less verbose date format. By default, a date format like2013-03-09T19:29:33.103897+01:00
is used. Since the kernel log contains a precision already (printk time) and the actual log time is irrelevant, I prefer something likeMar 9 19:29:13
.
- Since rsyslog should operate completely separated from systemd, remove the option that shares a socket with systemd:
sed 's/^Sockets=/#&/' /usr/lib/systemd/system/rsyslog.service | sudo tee /etc/systemd/system/rsyslog.service
- Next, make rsyslog start on boot and start it for this session by starting and enabling
rsyslog.service
.