syslog-ng
Contents
- 1 Note
- 2 Overview
- 3 Example configuration file
- 4 Sources
- 5 Destinations
- 6 Creating Filters for Messages
- 7 Log Paths
- 8 Tips and Tricks
- 9 External Links
Note
After upgrading to systemd, syslog-ng is unnecessary for most users and can be uninstalled, since the systemd journal provides this functionality.
Overview
syslog-ng takes incoming log messages from defined 'sources' and forwards them to the appropriate destinations, based on powerful filter directives. In a typical simple set-up, syslog-ng will read messages from three sources:
- the default
/dev/log
device, where most logs are sent - syslog-ng "internal" log messages
-
/proc/kmsg
kernel messages
Sources are defined using the "source" directive. These incoming messages are then filtered according to defined filters ("filter" keyword), i.e. according to originating program or log level, and sent to the appropriate "destination". Destinations include log files (e.g. /var/log/messages.log
), printing messages on a console and remote servers. The pivotal function is log. This function defines which filters should be applied to a certain source, and where the resulting messages should be sent to.
Example configuration file
For a quick start, here there is a classic configuration file slightly modified from the one in the
Gentoo Security Guide, the default syslog-ng.conf
provided with the source distribution, and my own personal preferences. This example includes logging from a chrooted bind source and logging to a remote server destination.
/etc/syslog-ng/syslog-ng.conf
@version: 3.0 # For a description of syslog-ng configuration file directives, please read # the syslog-ng Administrator's guide at: # # http://www.balabit.com/dl/html/syslog-ng-admin-guide_en.html/bk01-toc.html # ########################################################## # OPTIONS # options { create_dirs(yes); # use_dns(no); use_dns(persist_only); dns_cache_hosts(/etc/hosts); dns_cache_expire(87600); # disable the chained hostname format in logs (default is enabled) chain_hostnames(0); # the number of lines fitting in the output queue log_fifo_size(512); # enable or disable directory creation for destination files create_dirs(yes); # default owner, group, and permissions for log files (defaults are 0, 0, 0600) owner(root); group(log); perm(0640); # default owner, group, and permissions for created directories (defaults are 0, 0, 0700) dir_owner(root); dir_group(root); dir_perm(0740); # the time to wait before a died connection is re-established (default is 60) time_reopen(10); # the time to wait before an idle destination file is closed (default is 60) time_reap(360); # default no use_fqdn(no); keep_hostname(yes); # disable stats stats_freq(0); }; ########################################################## # SOURCES # source local_src { # message generated by syslog-ng internal(); # standard Linux log source (this is the default place for the syslog() function to send logs to) unix-stream("/dev/log"); # from a chrooted bind install unix-stream("/var/named/chroot/dev/log"); # messages from the kernel file("/proc/kmsg" program_override("kernel: ")); }; # source s_syslog { syslog(ip(127.0.0.1) port(1999) transport("tcp")); }; # source s_pipe { pipe("/dev/pipe" pad_size(2048)); }; ########################################################## # DESTINATIONS # destination d_file { file("/var/log/$YEAR.$MONTH.$DAY/everything.log" template("$HOUR:$MIN:$SEC [$LEVEL] [$FACILITY] [$PROGRAM] $MSG\n") template_escape(no)); }; destination d_askapacheloghost { tcp("askapacheloghost.dyndns.org" port(65514)); udp("askapacheloghost.dyndns.org" port(65514)); udp("askapacheloghost.dyndns.org" port(514)); }; destination d_authlog { file("/var/log/auth.log"); }; destination d_cron { file("/var/log/cron.log"); }; destination d_daemon { file("/var/log/daemon.log"); }; destination d_kern { file("/var/log/kern.log"); }; destination d_lpr { file("/var/log/lpr.log"); }; destination d_user { file("/var/log/user.log"); }; destination d_uucp { file("/var/log/uucp.log"); }; destination d_ppp { file("/var/log/ppp.log"); }; destination d_mail { file("/var/log/mail.log"); }; destination d_mailinfo { file("/var/log/mail.info"); }; destination d_mailwarn { file("/var/log/mail.warn"); }; destination d_mailerr { file("/var/log/mail.err"); }; destination d_newscrit { file("/var/log/news/news.crit"); }; destination d_newserr { file("/var/log/news/news.err"); }; destination d_newsnotice { file("/var/log/news/news.notice"); }; destination d_debug { file("/var/log/debug"); }; destination d_messages { file("/var/log/messages"); }; destination d_everything { file("/var/log/everything"); }; destination d_console { usertty("root"); }; destination d_console_all { file("/dev/tty12"); }; destination d_loghost { udp("loghost" port(999)); }; destination d_xconsole { pipe("/dev/xconsole"); }; ########################################################## # FILTERS # filter f_auth { facility(auth); }; filter f_authpriv { facility(auth, authpriv); }; filter f_syslog { program(syslog-ng); }; filter f_cron { facility(cron); }; filter f_daemon { facility(daemon); }; filter f_kernel { facility(kern) and not filter(f_iptables); }; filter f_lpr { facility(lpr); }; filter f_mail { facility(mail); }; filter f_news { facility(news); }; filter f_user { facility(user); }; filter f_uucp { facility(cron); }; filter f_news { facility(news); }; filter f_ppp { facility(local2); }; filter f_debug { not facility(auth, authpriv, news, mail); }; filter f_messages { level(info..warn) and not facility(auth, authpriv, mail, news, cron) and not program(syslog-ng) and not filter(f_iptables); }; filter f_everything { level(debug..emerg); }; filter f_emergency { level(emerg); }; filter f_info { level(info); }; filter f_notice { level(notice); }; filter f_warn { level(warn); }; filter f_crit { level(crit); }; filter f_err { level(err); }; filter f_iptables { match("IN=" value("MESSAGE")) and match("OUT=" value("MESSAGE")); }; filter f_acpid { program("acpid"); }; filter f_failed { match("failed" value(MESSAGE)); }; filter f_denied { match("denied" value(MESSAGE)); }; filter f_noshorewall { not match("Shorewall" value(MESSAGE)); }; # Filter everything except regex keyword Shorewall filter f_shorewall { match("Shorewall" value(MESSAGE)); }; # Filter regex keyword Shorewall ########################################################## # LOG # log { source(local_src); destination(d_askapacheloghost); }; log { source(local_src); destination(d_file); }; log { source(local_src); filter(f_authpriv); destination(d_authlog); }; log { source(local_src); filter(f_user); destination(d_user); }; log { source(local_src); filter(f_cron); destination(d_cron); }; log { source(local_src); filter(f_daemon); destination(d_daemon); }; log { source(local_src); filter(f_kern); destination(d_kern); }; log { source(local_src); filter(f_lpr); destination(d_lpr); }; log { source(local_src); filter(f_mail); destination(d_mail); }; log { source(local_src); filter(f_uucp); destination(d_uucp); }; log { source(local_src); filter(f_mail); filter(f_info); destination(d_mailinfo); }; log { source(local_src); filter(f_mail); filter(f_warn); destination(d_mailwarn); }; log { source(local_src); filter(f_mail); filter(f_err); destination(d_mailerr); }; log { source(local_src); filter(f_news); filter(f_crit); destination(d_newscrit); }; log { source(local_src); filter(f_news); filter(f_err); destination(d_newserr); }; log { source(local_src); filter(f_news); filter(f_notice); destination(d_newsnotice); }; log { source(local_src); filter(f_debug); destination(d_debug); }; log { source(local_src); filter(f_messages); destination(d_messages); }; log { source(local_src); filter(f_ppp); destination(d_ppp); }; log { source(local_src); destination(d_messages); }; #default log log { source(local_src); destination(console_all); };
Sources
syslog-ng receives log messages from a source. To define a source you should follow the following syntax:
source <identifier> { source-driver(params); source-driver(params); ... };
You can look at the identifiers and source-drivers in the official manuals. This will follow the manual to explain the configuration file above. The unix-stream() source-driver opens the given AF_UNIX socket and starts listening on it for messages. The internal() source-driver gets messages generated by syslog-ng.
Therefore, the following means: src
gets messages from the /dev/log
socket and syslog-ng.
source src { unix-stream("/dev/log"); internal(); };
The kernel sends log messages to /proc/kmsg
and the file() driver reads log messages from files. Therefore, the following means:
kernsrc gets messages from file /proc/kmsg
source kernsrc { file("/proc/kmsg"); };
In the default configuration file after emerging syslog-ng, the source is defined as:
source src { unix-stream("/dev/log"); internal(); pipe("/proc/kmsg"); };
Reading messages by pipe("/proc/kmsg")
gives a better performance but because it opens its argument in read-write mode can be a security
hazard as the syslog-ng admin guide states in section 3.3.3:
"Pipe is very similar to the file() driver, but there are a few differences, for example pipe() opens its argument in read-write mode, therefore it is not recommended to be used on special files like /proc/kmsg
." (You can follow this discussion in this post.)
To open a port to read data from a remote server a source must be defined with this syntax:
source s_net { udp(); };
for UDP or
source s_net { tcp(); };
to receive log messages via TCP. Both listen on port 514.
Destinations
In syslog-ng, log messages are sent to files. The syntax is very similar to sources:
destination <identifier> {destination-driver(params); destination-driver(params); ... };
You will be normally logging to a file, but you could log to a different destination-driver: pipe, Unix socket, TCP-UDP ports,
terminals or to specific programs. Therefore, this means sending authlog messages to /var/log/auth.log
:
destination authlog { file("/var/log/auth.log"); };
If the user is logged in, usertty()
sends messages to the terminal of the specified user. If you want to send console messages
to root's terminal if it is logged in:
destination console { usertty("root"); };
Messages can be sent to a pipe with pipe()
. The following sends xconsole messages to the pipe /dev/xconsole
.
This needs some more configuration, so you could look at the sub-section xconsole below.
destination xconsole { pipe("/dev/xconsole"); };
To send messages on the network, use udp()
. The following will send your log data out to another server.
destination remote_server { udp("10.0.0.2" port(514)); };
Creating Filters for Messages
The syntax for the filter statement is:
filter <identifier> { expression; };
Functions can be used in the expression, such as the function facility()
which selects messages based on the facility codes.
The Linux kernel has a few facilities you can use for logging. Each facility has a log-level; where debug is the most verbose,
and panic only shows serious errors. You can find the facilities, log levels and priority names in /usr/include/sys/syslog.h
.
To filter those messages coming from authorization, like
May 11 23:42:31 mimosinnet su(pam_unix)[18569]: session opened for user root by (uid=1000), use the following:
filter f_auth { facility(auth); };
The facility expression can use the boolean operators and
, or
, and not
, so the following filter
selects those messages not coming from authorization, network news or mail:
filter f_debug { not facility(auth, authpriv, news, mail); };
The function level()
selects messages based on its priority level, so if you want to select informational levels:
filter f_info { level(info); };
Functions and boolean operators can be combined in more complex expressions. The following line filters messages with a priority level from informational to warning not coming from auth, authpriv, mail and news facilities:
filter f_messages { level(info..warn) and not facility(auth, authpriv, mail, news); };
Messages can also be selected by matching a regular expression in the message with the function match("regex" value("keyword"))
. For example:
filter f_failed { match("regex" value("failed")); };
To filter messages received from a particular remote host, the host()
function must be used:
filter f_host { host( "192.168.1.1" ); };
Log Paths
syslog-ng connects sources, filters and destinations with log statements. The syntax is:
log {source(s1); source(s2); ... filter(f1); filter(f2); ... destination(d1); destination(d2); ... flags(flag1[, flag2...]); };
The following for example sends messages from src
source to mailinfo
destination filtered by f_info
filter.
log { source(src); filter(f_mail); filter(f_info); destination(mailinfo); };
Tips and Tricks
After understanding the logic behind syslog-ng, many possible and complex configuration are possible. Here there are some examples.
Have syslog-ng reload the configuration file
You can make syslog-ng re-evaluate the configuration file. You can do so manually by sending a SIGHUP
to the process, or call the reload function with systemctl:
# systemctl reload syslog-ng
Failover Logging to Remote Host
This setup shows how to send the default unencrypted syslog packets across both TCP and UDP protocols, using the standard port (514) and an alternate port. This is sending the same output to the same machine 4 different ways to try and make sure packets make it. Mostly useful if you are debugging a remote server that fails to reboot. The different ports and protocols are to make it past any firewall filters or other network problems. Also useful for port-forwarding and using tunnels. Something like this setup is ideal to tunnel across an ssh connection that the prone-to-failover host initiates through a reverse connection.
#sending to a remote syslog server on TCP and UDP ports (not encrypted) destination askapache_failover_loghost { tcp("208.86.158.195" port(25214)); udp("208.86.158.195" port(25214)); udp("mysyslog1.dyndns.org" port(514)); }; log { source(src); destination(askapache_failover_loghost); };
And then on the loghost receiving these logs:
#a USB redirected console for flexible viewing destination debugging_console { file("/dev/ttyU1"); }; # listens on IP addresses and ports, sets the incoming settings source prone_to_failover_host { tcp(ip(208.86.158.195),port(25214)); udp(ip(208.86.158.195) port(25214)); udp(default-facility(syslog) default-priority(emerg)); tcp(default-facility(syslog) default-priority(emerg)); } # log it log { source(prone_to_failover_host); destination(debugging_console); };
Move log to another file
In order to move some log from /var/log/messages
to another file:
#sshd configuration destination ssh { file("/var/log/ssh.log"); }; filter f_ssh { program("sshd"); }; log { source(src); filter(f_ssh); destination(ssh); };
Configuring as a loghost
Configuring your system to be a loghost is quite simple. Drop the following into your configuration, and create the needed directory.
With this simple configuration, log filenames will be based on the FQDN of the remote host,
and located in /var/log/remote/
. After creating the remote directory, reload your syslog-ng configuration.
source net { udp(); }; destination remote { file("/var/log/remote/$FULLHOST"); }; log { source(net); destination(remote); };
Improve Performance
syslog-ng's performance can be improved in different ways:
Write every so often
It seems that the old sync(X)
option is called flush_lines(X)
now, where the writing to the file is buffered for X
lines. Default is 0 (no buffering).
Avoid redundant processing and disk space
A single log message can be sent to different log files several times. For example, in the initial configuration file, we have the following definitions:
destination cron { file("/var/log/cron.log"); }; destination messages { file("/var/log/messages"); }; filter f_cron { facility(cron); }; filter f_messages { level(info..warn) and not facility(auth, authpriv, mail, news); }; log { source(src); filter(f_cron); destination(cron); }; log { source(src); filter(f_messages); destination(messages); };
The same message from the cron
facility will end up in both the cron.log
and messages
files. To change this behavior we can use the final
flag,
ending up further processing with the message. Therefore, in this example, if we want messages from the cron
facility not ending up in the
messages file, we should change the cron's log sentence by:
log { source(src); filter(f_cron); destination(cron); flags(final); };
another way is to exclude the cron
facility from f_messages
filter:
filter f_messages { level(info..warn) and not facility(cron, auth, authpriv, mail, news); };
PostgreSQL Destination
This section will use two roles: syslog
and logwriter
. syslog
will be the administrator of the database syslog
and logwriter
will only be able to add records to the logs
table.
No longer needed to create table for logs. syslog-ng will create automatically.
psql -U postgres
postgres=# CREATE ROLE syslog WITH LOGIN; postgres=# \password syslog # Using the \password function is secure because postgres=# \password logwriter # the password isn't saved in history. postgres=# CREATE DATABASE syslog OWNER syslog; postgres=# \q # You're done here for the moment
Edit pg_hba.conf
to allow syslog
and logwriter
to establish a connection to PostgreSQL.
/var/lib/postgresql/8.4/data/pg_hba.conf
# TYPE DATABASE USER CIDR-ADDRESS METHOD host syslog logwriter 192.168.0.1/24 md5 host syslog syslog 192.168.0.10/32 md5
Tell PostgreSQL to reload the configuration files:
/etc/rc.d/postgresql-8.4 reload
Edit /etc/syslog-ng.conf
so that it knows where and how to write to PostgreSQL. syslog-ng will utilize the logwriter
role.
... # # SQL logging support # destination d_pgsql { sql(type(pgsql) host("127.0.0.1") username("logwriter") password("password") database("syslog") table("logs_${HOST}_${R_YEAR}${R_MONTH}${R_DAY}") #or whatever you want, example ${HOST}" for hosts, ${LEVEL}" for levels.. etc columns("datetime timestamp with time zone", "host varchar(32)", "program varchar(16)", "pid varchar(16)", "message varchar(200)") values("$R_ISODATE", "$HOST", "$PROGRAM", "$PID", "$MSG") indexes("datetime", "host", "program", "pid", "message")); }; log { source(src); destination(d_pgsql); };
Finally, restart syslog-ng.
/etc/rc.d/syslog-ng restart
And check to see if things are being logged.
psql -U logwriter -d syslog syslog=> SELECT * FROM <your table name> ORDER BY datetime DESC LIMIT 10;
ISO 8601 timestamps
Before :
#logger These timestamps are not optimal. #tail -n 1 /var/log/messages.log Feb 18 14:25:01 hostname logger: These timestamps are not optimal. #
Add ts_format(iso);
to /etc/syslog-ng/syslog-ng.conf
in the options section. Example:
options { stats_freq (0); flush_lines (0); time_reopen (10); log_fifo_size (1000); long_hostnames(off); use_dns (no); use_fqdn (no); create_dirs (no); keep_hostname (yes); perm(0640); group("log"); ts_format(iso); #make ISO-8601 timestamps };
Then:
# /etc/rc.d/syslog-ng reload
After :
#logger Now THAT is a timestamp! #tail -n 2 /var/log/messages.log Feb 18 14:25:01 hostname logger: These timestamps are not optimal. 2010-02-18T20:23:58-05:00 electron logger: Now THAT is a timestamp! #
RFC 3339 timestamps
Same as above, except use rfc3339
instead of iso
for ts_format
Log Levels
Log levels are defined separately for each logged facility in syslog-ng config. Available log levels are listed in /usr/include/sys/syslog.h :
define LOG_EMERG 0 /* system is unusable */ define LOG_ALERT 1 /* action must be taken immediately */ define LOG_CRIT 2 /* critical conditions */ define LOG_ERR 3 /* error conditions */ define LOG_WARNING 4 /* warning conditions */ define LOG_NOTICE 5 /* normal but significant condition */ define LOG_INFO 6 /* informational */ define LOG_DEBUG 7 /* debug-level messages */
See Also
- Netconsole A kernel module that sends all kernel log messages (i.e. dmesg) over the network to another computer, without involving user space (e.g. syslogd).
External Links
- syslog-ng OSE Project Page
- Portal to syslog-ng Documentation
- syslog-ng Project Page on Freshmeat
- Gentoo syslog-ng wiki
- Gentoo Security Handbook on Logging
- Syslog Logging with PostgreSQL HOWTO
- ISO_8601 Wikipedia page for ISO 8601
- RFC 3164 - The BSD syslog Protocol
- RFC 5424 - The Syslog Protocol
- RFC 3339 - Date and Time on the Internet: Timestamps