Difference between revisions of "Rsyslog"
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== Installation == | == Installation == | ||
− | [[pacman|install]] the {{Pkg|rsyslog}} package which is available in the [[ | + | [[pacman|install]] the {{Pkg|rsyslog}} package which is available in the [[official repositories]]. |
=== Configure Hostname === | === Configure Hostname === |
Revision as of 01:51, 20 March 2014
rsyslog is an alternative logger to syslog-ng and offers many benefits over syslog-ng. rsyslog is also the default logger for the latest versions of Red Hat Enterprise Linux, as well as many other Linux distributions. Many of rsyslog's benefits over syslog-ng can be found here.
Contents
Installation
install the rsyslog package which is available in the official repositories.
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
Activation
After installing rsyslog, systemd will need to know about the service file packaged with rsyslog:
# systemctl daemon-reload
Disable your old logger, (usually syslog-ng), then enable and start the new service:
# systemctl {disable|stop} syslog-ng # systemctl {enable|start} rsyslog
Configuration
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 syslog-ng
s behavior for the old auth.log
:
/etc/rsyslog.conf
auth.* -/var/log/auth
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. |
A common mnemonic used to remember the syslog levels in reverse order: "Do I Notice When Evenings Come Around Early".
See also: http://www.rsyslog.com/doc/manual.html
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:
sudo systemctl enable rsyslog.service
sudo systemctl start rsyslog.service
/proc/kmsg
. This means that subsequent reads from that file (either the user or a syslog daemon) will not read "old" logs from that file anymore. journald is not affected as it reads from /dev/kmsg
which allows multiple readers.