Generating and reading system logs is an important aspect of system administration. The information in system logs can be used to detect hardware and software issues as well as application and system configuration errors. This information also plays an important role in security auditing and incident response. Most system daemons and applications will generate log entries.
FreeBSD provides a system logger,
syslogd, to manage logging. By
default, syslogd is started when the
system boots. This is controlled by the variable
syslogd_enable in
/etc/rc.conf. There are numerous
application arguments that can be set using
syslogd_flags in
/etc/rc.conf. Refer to syslogd(8) for
more information on the available arguments.
This section describes how to configure the FreeBSD system logger for both local and remote logging and how to perform log rotation and log management.
The configuration file,
/etc/syslog.conf, controls what
syslogd does with log entries as
they are received. There are several parameters to control
the handling of incoming events. The
facility describes which subsystem
generated the message, such as the kernel or a daemon, and the
level describes the severity of the
event that occurred. This makes it possible to configure if
and where a log message is logged, depending on the facility
and level. It is also possible to take action depending on
the application that sent the message, and in the case of
remote logging, the hostname of the machine generating the
logging event.
This configuration file contains one line per action,
where the syntax for each line is a selector field followed by
an action field. The syntax of the selector field is
facility.level which will match log
messages from facility at level
level or higher. It is also
possible to add an optional comparison flag before the level
to specify more precisely what is logged. Multiple selector
fields can be used for the same action, and are separated with
a semicolon (;). Using
* will match everything. The action field
denotes where to send the log message, such as to a file or
remote log host. As an example, here is the default
syslog.conf from FreeBSD:
# $FreeBSD$ # # Spaces ARE valid field separators in this file. However, # other *nix-like systems still insist on using tabs as field # separators. If you are sharing this file between systems, you # may want to use only tabs as field separators here. # Consult the syslog.conf(5) manpage. *.err;kern.warning;auth.notice;mail.crit /dev/console *.notice;authpriv.none;kern.debug;lpr.info;mail.crit;news.err /var/log/messages security.* /var/log/security auth.info;authpriv.info /var/log/auth.log mail.info /var/log/maillog lpr.info /var/log/lpd-errs ftp.info /var/log/xferlog cron.* /var/log/cron !-devd *.=debug /var/log/debug.log *.emerg * # uncomment this to log all writes to /dev/console to /var/log/console.log #console.info /var/log/console.log # uncomment this to enable logging of all log messages to /var/log/all.log # touch /var/log/all.log and chmod it to mode 600 before it will work #*.* /var/log/all.log # uncomment this to enable logging to a remote loghost named loghost #*.* @loghost # uncomment these if you're running inn # news.crit /var/log/news/news.crit # news.err /var/log/news/news.err # news.notice /var/log/news/news.notice # Uncomment this if you wish to see messages produced by devd # !devd # *.>=info !ppp *.* /var/log/ppp.log !*
In this example:
Line 8 matches all messages with a level of
err or higher, as well as
kern.warning,
auth.notice and
mail.crit, and sends these log messages
to the console
(/dev/console).
Line 12 matches all messages from the
mail facility at level
info or above and logs the messages to
/var/log/maillog.
Line 17 uses a comparison flag (=)
to only match messages at level debug
and logs them to
/var/log/debug.log.
Line 33 is an example usage of a program
specification. This makes the rules following it only
valid for the specified program. In this case, only the
messages generated by ppp are
logged to /var/log/ppp.log.
The available levels, in order from most to least
critical are emerg,
alert, crit,
err, warning,
notice, info, and
debug.
The facilities, in no particular order, are
auth, authpriv,
console, cron,
daemon, ftp,
kern, lpr,
mail, mark,
news, security,
syslog, user,
uucp, and local0 through
local7. Be aware that other operating
systems might have different facilities.
To log everything of level notice and
higher to /var/log/daemon.log, add the
following entry:
daemon.notice /var/log/daemon.log
For more information about the different levels and
facilities, refer to syslog(3) and syslogd(8).
For more information about
/etc/syslog.conf, its syntax, and more
advanced usage examples, see syslog.conf(5).
Log files can grow quickly, taking up disk space and making it more difficult to locate useful information. Log management attempts to mitigate this. In FreeBSD, newsyslog is used to manage log files. This built-in program periodically rotates and compresses log files, and optionally creates missing log files and signals programs when log files are moved. The log files may be generated by syslogd or by any other program which generates log files. While newsyslog is normally run from cron(8), it is not a system daemon. In the default configuration, it runs every hour.
To know which actions to take,
newsyslog reads its configuration
file, /etc/newsyslog.conf. This file
contains one line for each log file that
newsyslog manages. Each line
states the file owner, permissions, when to rotate that file,
optional flags that affect log rotation, such as compression,
and programs to signal when the log is rotated. Here is the
default configuration in FreeBSD:
# configuration file for newsyslog # $FreeBSD: release/10.2.0/en_US.ISO8859-1/books/handbook/config/chapter.xml 46735 2015-05-29 23:24:13Z allanjude $ # # Entries which do not specify the '/pid_file' field will cause the # syslogd process to be signalled when that log file is rotated. This # action is only appropriate for log files which are written to by the # syslogd process (ie, files listed in /etc/syslog.conf). If there # is no process which needs to be signalled when a given log file is # rotated, then the entry for that file should include the 'N' flag. # # The 'flags' field is one or more of the letters: BCDGJNUXZ or a '-'. # # Note: some sites will want to select more restrictive protections than the # defaults. In particular, it may be desirable to switch many of the 644 # entries to 640 or 600. For example, some sites will consider the # contents of maillog, messages, and lpd-errs to be confidential. In the # future, these defaults may change to more conservative ones. # # logfilename [owner:group] mode count size when flags [/pid_file] [sig_num] /var/log/all.log 600 7 * @T00 J /var/log/amd.log 644 7 100 * J /var/log/auth.log 600 7 100 @0101T JC /var/log/console.log 600 5 100 * J /var/log/cron 600 3 100 * JC /var/log/daily.log 640 7 * @T00 JN /var/log/debug.log 600 7 100 * JC /var/log/kerberos.log 600 7 100 * J /var/log/lpd-errs 644 7 100 * JC /var/log/maillog 640 7 * @T00 JC /var/log/messages 644 5 100 @0101T JC /var/log/monthly.log 640 12 * $M1D0 JN /var/log/pflog 600 3 100 * JB /var/run/pflogd.pid /var/log/ppp.log root:network 640 3 100 * JC /var/log/devd.log 644 3 100 * JC /var/log/security 600 10 100 * JC /var/log/sendmail.st 640 10 * 168 B /var/log/utx.log 644 3 * @01T05 B /var/log/weekly.log 640 5 1 $W6D0 JN /var/log/xferlog 600 7 100 * JC
Each line starts with the name of the log to be rotated,
optionally followed by an owner and group for both rotated and
newly created files. The mode field sets
the permissions on the log file and count
denotes how many rotated log files should be kept. The
size and when fields
tell newsyslog when to rotate the
file. A log file is rotated when either its size is larger
than the size field or when the time in the
when filed has passed. An asterisk
(*) means that this field is ignored. The
flags field gives further
instructions, such as how to compress the rotated file or to
create the log file if it is missing. The last two fields are
optional and specify the name of the Process ID
(PID) file of a process and a signal number
to send to that process when the file is rotated.
For more information on all fields, valid flags, and how to specify the rotation time, refer to newsyslog.conf(5). Since newsyslog is run from cron(8), it cannot rotate files more often than it is scheduled to run from cron(8).
Monitoring the log files of multiple hosts can become unwieldy as the number of systems increases. Configuring centralized logging can reduce some of the administrative burden of log file administration.
In FreeBSD, centralized log file aggregation, merging, and
rotation can be configured using
syslogd and
newsyslog. This section
demonstrates an example configuration, where host
A, named logserv.example.com, will
collect logging information for the local network. Host
B, named logclient.example.com,
will be configured to pass logging information to the logging
server.
A log server is a system that has been configured to accept logging information from other hosts. Before configuring a log server, check the following:
If there is a firewall between the logging server and any logging clients, ensure that the firewall ruleset allows UDP port 514 for both the clients and the server.
The logging server and all client machines must
have forward and reverse entries in the local
DNS. If the network does not have a
DNS server, create entries in each
system's /etc/hosts. Proper name
resolution is required so that log entries are not
rejected by the logging server.
On the log server, edit
/etc/syslog.conf to specify the name of
the client to receive log entries from, the logging facility
to be used, and the name of the log to store the host's log
entries. This example adds the hostname of
B, logs all facilities, and stores
the log entries in
/var/log/logclient.log.
When adding multiple log clients, add a similar two-line entry for each client. More information about the available facilities may be found in syslog.conf(5).
Next, configure
/etc/rc.conf:
syslogd_enable="YES" syslogd_flags="-a logclient.example.com -v -v"
The first entry starts
syslogd at system boot. The
second entry allows log entries from the specified client.
The -v -v increases the verbosity of logged
messages. This is useful for tweaking facilities as
administrators are able to see what type of messages are
being logged under each facility.
Multiple -a options may be specified to
allow logging from multiple clients. IP
addresses and whole netblocks may also be specified. Refer
to syslogd(8) for a full list of possible
options.
Finally, create the log file:
#touch /var/log/logclient.log
At this point, syslogd should be restarted and verified:
#service syslogd restart#pgrep syslog
If a PID is returned, the server
restarted successfully, and client configuration can begin.
If the server did not restart, consult
/var/log/messages for the error.
A logging client sends log entries to a logging server on the network. The client also keeps a local copy of its own logs.
Once a logging server has been configured, edit
/etc/rc.conf on the logging
client:
syslogd_enable="YES" syslogd_flags="-s -v -v"
The first entry enables
syslogd on boot up. The second
entry prevents logs from being accepted by this client from
other hosts (-s) and increases the
verbosity of logged messages.
Next, define the logging server in the client's
/etc/syslog.conf. In this example, all
logged facilities are sent to a remote system, denoted by
the @ symbol, with the specified
hostname:
*.* @logserv.example.com
After saving the edit, restart syslogd for the changes to take effect:
#service syslogd restart
To test that log messages are being sent across the network, use logger(1) on the client to send a message to syslogd:
#logger "Test message from logclient"
This message should now exist both in
/var/log/messages on the client and
/var/log/logclient.log on the log
server.
If no messages are being received on the log server, the
cause is most likely a network connectivity issue, a
hostname resolution issue, or a typo in a configuration
file. To isolate the cause, ensure that both the logging
server and the logging client are able to
ping each other using the hostname
specified in their /etc/rc.conf. If
this fails, check the network cabling, the firewall ruleset,
and the hostname entries in the DNS
server or /etc/hosts on both the
logging server and clients. Repeat until the
ping is successful from both
hosts.
If the ping succeeds on both hosts
but log messages are still not being received, temporarily
increase logging verbosity to narrow down the configuration
issue. In the following example,
/var/log/logclient.log on the logging
server is empty and /var/log/messages
on the logging client does not indicate a reason for the
failure. To increase debugging output, edit the
syslogd_flags entry on the logging server
and issue a restart:
syslogd_flags="-d -a logclien.example.com -v -v"
#service syslogd restart
Debugging data similar to the following will flash on the console immediately after the restart:
logmsg: pri 56, flags 4, from logserv.example.com, msg syslogd: restart syslogd: restarted logmsg: pri 6, flags 4, from logserv.example.com, msg syslogd: kernel boot file is /boot/kernel/kernel Logging to FILE /var/log/messages syslogd: kernel boot file is /boot/kernel/kernel cvthname(192.168.1.10) validate: dgram from IP 192.168.1.10, port 514, name logclient.example.com; rejected in rule 0 due to name mismatch.
In this example, the log messages are being rejected due
to a typo which results in a hostname mismatch. The
client's hostname should be logclient,
not logclien. Fix the typo, issue a
restart, and verify the results:
#service syslogd restartlogmsg: pri 56, flags 4, from logserv.example.com, msg syslogd: restart syslogd: restarted logmsg: pri 6, flags 4, from logserv.example.com, msg syslogd: kernel boot file is /boot/kernel/kernel syslogd: kernel boot file is /boot/kernel/kernel logmsg: pri 166, flags 17, from logserv.example.com, msg Dec 10 20:55:02 <syslog.err> logserv.example.com syslogd: exiting on signal 2 cvthname(192.168.1.10) validate: dgram from IP 192.168.1.10, port 514, name logclient.example.com; accepted in rule 0. logmsg: pri 15, flags 0, from logclient.example.com, msg Dec 11 02:01:28 trhodes: Test message 2 Logging to FILE /var/log/logclient.log Logging to FILE /var/log/messages
At this point, the messages are being properly received and placed in the correct file.
As with any network service, security requirements should be considered before implementing a logging server. Log files may contain sensitive data about services enabled on the local host, user accounts, and configuration data. Network data sent from the client to the server will not be encrypted or password protected. If a need for encryption exists, consider using security/stunnel, which will transmit the logging data over an encrypted tunnel.
Local security is also an issue. Log files are not
encrypted during use or after log rotation. Local users may
access log files to gain additional insight into system
configuration. Setting proper permissions on log files is
critical. The built-in log rotator,
newsyslog, supports setting
permissions on newly created and rotated log files. Setting
log files to mode 600 should prevent
unwanted access by local users. Refer to
newsyslog.conf(5) for additional information.
All FreeBSD documents are available for download at http://ftp.FreeBSD.org/pub/FreeBSD/doc/
Questions that are not answered by the
documentation may be
sent to <[email protected]>.
Send questions about this document to <[email protected]>.