Syslog levels are a method of describing to syslog (8) the importance of a message. A number of Shorewall parameters have a syslog level as their value.

Valid levels are:

For most Shorewall logging, a level of 6 (info) is appropriate. Shorewall log messages are generated by Netfilter and are logged using the kern facility and the level that you specify. If you are unsure of the level to choose, 6 (info) is a safe bet. You may specify levels by name or by number.

Beginning with Shorewall 4.5.5, the level name or number may be optionally followed by a comma-separated list of one or more log options. The list is enclosed in parentheses. Log options cause additional information to be included in each log message.

Valid log options are:

Example: info(tcp_options,tcp_sequence)

Syslogd writes log messages to files (typically in /var/log/*) based on their facility and level. The mapping of these facility/level pairs to log files is done in /etc/syslog.conf (5). If you make changes to this file, you must restart syslogd before the changes can take effect.

Syslog may also write to your system console. See Shorewall FAQ 16 for ways to avoid having Shorewall messages written to the console.

There are a couple of limitations to syslogd-based logging:

If your kernel has ULOG target support (and most vendor-supplied kernels do), you may also specify a log level of ULOG (must be all caps). When ULOG is used, Shorewall will direct Netfilter to log the related messages via the ULOG target which will send them to a process called “ulogd”. The ulogd program is included in most distributions and is also available from http://www.netfilter.org/projects/ulogd/index.html. Ulogd can be configured to log all Shorewall messages to their own log file.

You will need to change all instances of log levels (usually “info”) in your Shorewall configuration files to “ULOG” - this includes entries in the policy, rules and shorewall.conf files. Here's what I had at one time:

gateway:/etc/shorewall# grep -v ^\# * | egrep '\$LOG|ULOG|LOGFILE'
params:LOG=ULOG
policy:loc              $FW             REJECT          $LOG
policy:net              all             DROP            $LOG            10/sec:40
policy:all              all             REJECT          $LOG
rules:REJECT:$LOG       loc                             net                     tcp     25
rules:REJECT:$LOG       loc                             net                     udp     1025:1031
rules:REJECT:$LOG       dmz                             net                     udp     1025:1031
rules:ACCEPT:$LOG       dmz                             net                     tcp     1024:                                   20
rules:REJECT:$LOG       $FW                             net                     udp     1025:1031
shorewall.conf:LOGFILE=/var/log/shorewall
shorewall.conf:LOGUNCLEAN=$LOG
shorewall.conf:MACLIST_LOG_LEVEL=$LOG
shorewall.conf:TCP_FLAGS_LOG_LEVEL=$LOG
shorewall.conf:RFC1918_LOG_LEVEL=$LOG
gateway:/etc/shorewall#                                               

Finally edit /etc/shorewall/shorewall.conf and set LOGFILE=<file that you wish to log to>. This tells the /sbin/shorewall program where to look for the log when processing its “show log”, “logwatch” and “dump” commands.

The NFLOG target, a successor to ULOG, is supported shorewall. Both ULOG and NFLOG may be followed by a list of up to three numbers in parentheses.

Examples:

/etc/shorewall/shorewall.conf:

MACLIST_LOG_LEVEL=NFLOG(1,0,1)

/etc/shorewall/rules:

#ACTION             SOURCE     DEST     PROTO     DEST
#                                                 PORT(S)
ACCEPT:NFLOG(1,0,1) vpn        fw       tcp       ssh,time,631,8080