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SYSLOG.CONF(5) NetBSD File Formats Manual SYSLOG.CONF(5)
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syslog.conf -- syslogd(8) configuration file
The syslog.conf file is the configuration file for the syslogd(8) pro-
gram. It consists of extended options (lines with one key="value"
assignment) and blocks of lines separated by program and hostname speci-
fications, with each line containing two fields: the selector field which
specifies the types of messages and priorities to which the line applies,
and an action field which specifies the action to be taken if a message
syslogd(8) receives matches the selection criteria. The selector field
is separated from the action field by one or more tab characters.
The Selectors function are encoded as a facility, a period (`.'), an
optional set of comparison flags ([!] [<=>]), and a level, with no inter-
vening white-space. Both the facility and the level are case insensi-
The facility describes the part of the system generating the message, and
is one of the following keywords: auth, authpriv, cron, ftp, daemon,
kern, lpr, mail, mark, news, syslog, user, uucp and local0 through
local7. These keywords (with the exception of mark) correspond to the
similar ``LOG_'' values specified to the openlog(3) and syslog(3) library
The comparison flags may be used to specify exactly what levels are
logged. If unspecified, the default comparison is `>=' (greater than or
equal to), or, if the -U option is passed to syslogd(8), `=' (equal to).
Comparison flags beginning with `!' will have their logical sense
inverted. Thus, `!=info' means all levels except info and `!notice' has
the same meaning as `<notice'.
The level describes the severity of the message, and is a keyword from
the following ordered list (higher to lower): emerg, alert, crit, err,
warning, notice, info and debug. These keywords correspond to the simi-
lar (LOG_) values specified to the syslog(3) library routine.
Each block of lines is separated from the previous block by a program or
hostname specification. A block will only log messages corresponding to
the most recent program and hostname specifications given. Consider the
case of a block that selects `pppd' as the program, directly followed by
a block that selects messages from the hostname `dialhost'. The second
block will log only messages from the pppd(8) program from the host
A program specification of the form `#!+prog1,prog2' or `!+prog1,prog2'
will cause subsequent blocks to be applied to messages logged by the
specified programs. A program specification of the form `#!-prog1,prog2'
or `!-prog1,prog2' will cause subsequent blocks to be applied to messages
logged by programs other than the ones specified. A program specifica-
tion of the form `#!prog1,prog2' or `!prog1,prog2' is equivalent to
`!+prog1,prog2'. Program selectors may also match kernel-generated mes-
sages. For example, a program specification of `!+subsys' will match
kernel-generated messages of the form `subsys: here is a message'. The
special specification `!*' will cause subsequent blocks to apply to all
A hostname specification of the form `#+host1,host2' or `+host1,host2'
will cause subsequent blocks to be applied to messages received from the
specified hosts. A hostname specification of the form `#-host1,host2' or
`-host1,host2' will cause subsequent blocks to be applied to messages
from hosts other than the ones specified. If the hostname is given as
`@', the local hostname will be used. The special specification `+*'
will cause subsequent blocks to apply to all hosts.
See syslog(3) for a further descriptions of both the facility and level
keywords and their significance. It is preferred that selections be made
based on facility rather than program, since the latter can vary in a
networked environment. However, there are cases where a facility may be
too broadly defined.
If a received message matches the specified facility, and the specified
level comparison is true, and the first word in the message after the
date matches the program, the action specified in the action field will
Multiple selectors may be specified for a single action by separating
them with semicolon (`;') characters. It is important to note, however,
that each selector can modify the ones preceding it.
Multiple facilities may be specified for a single level by separating
them with comma (`,') characters.
An asterisk (`*') can be used to specify all facilities or all levels.
The special facility ``mark'' receives a message at priority ``info''
every 20 minutes (see syslogd(8)). This is not enabled by a facility
field containing an asterisk.
The special level ``none'' disables a particular facility.
The action field of each line specifies the action to be taken when the
selector field selects a message. There are five forms:
· A pathname (beginning with a leading slash). Selected messages are
appended to the file, unless pathname points to an existing FIFO spe-
cial file. syslogd(8) treats FIFO specially by opening them in non-
blocking mode and discarding messages sent when no reader is listen-
ing on the other side.
To ensure that kernel messages are written to disk promptly,
syslogd(8) calls fsync(2) after writing messages from the kernel.
Other messages are not synced explicitly. You may disable syncing of
files specified to receive kernel messages by prefixing the pathname
with a minus sign `-'. Note that use of this option may cause the
loss of log information in the event of a system crash immediately
following the write attempt. However, using this option may prove to
be useful if your system's kernel is logging many messages.
Normally the priority and version is not written to file. In order
to use syslog-sign you may prefix a pathname with the plus sign `+'.
If both switches are used the order has to be `+-'.
· A hostname (preceded by an at (`@') sign). Selected messages are
forwarded to the syslogd(8) program on the named host with UDP.
· A hostname preceded by an at (`@') sign and enclosed in brackets
(`') Selected messages are forwarded with TLS to the syslogd(8)
program on the named host. After the closing bracket a colon (`:')
and a port or service name may be appended. Additional options are
configured in parentheses in the form of key="value". Recognized
keywords are subject, fingerprint, cert, and verify.
· A comma separated list of users. Selected messages are written to
those users if they are logged in.
· An asterisk. Selected messages are written to all logged-in users.
· A vertical bar (`|') followed by a command to which to pipe the
selected messages. The command string is passed to /bin/sh for eval-
uation, so the usual shell metacharacters or input/output redirection
can occur. (Note that redirecting stdio(3) buffered output from the
invoked command can cause additional delays, or even lost output data
in case a logging subprocess exits with a signal.) The command
itself runs with stdout and stderr redirected to /dev/null. Upon
receipt of a SIGHUP, syslogd(8) will close the pipe to the process.
If the process does not exit voluntarily, it will be sent a SIGTERM
signal after a grace period of up to 60 seconds.
The command will only be started once data arrives that should be
piped to it. If the command exits, it will be restarted as neces-
If it is desired that the subprocess should receive exactly one line
of input, this can be achieved by exiting after reading and process-
ing the single line. A wrapper script can be used to achieve this
effect, if necessary. Note that this method can be very resource-
intensive if many log messages are being piped through the filter.
Unless the command is a full pipeline, it may be useful to start the
command with exec so that the invoking shell process does not wait
for the command to complete. Note that the command is started with
the UID of the syslogd(8) process, normally the superuser.
Just like with files a plus sign `+' will leave the priority and ver-
sion information intact.
Blank lines and lines whose first non-blank character is a hash (`#')
character are ignored.
Additional options are used for TLS configuration:
Enables TLS server mode.
Service name or port number to bind to. Default is `syslog'. As long as
no official port is assigned this option is required for TLS servers.
Hostname or IP to bind to.
Automatically generate a private key and certificate.
File with private key. Default is `/etc/openssl/default.key'
File with certificate to use. Default is `/etc/openssl/default.crt'
File with CA certificate to use.
Directory containing CA certificates.
If set to `off' then certificate authentication is skipped.
List of fingerprints of trusted client certificates.
List of filenames with trusted client certificates.
One function of TLS is mutual authentication of client and server.
Unless authentication is disabled by setting `tls_verify=off' the follow-
ing rules are used:
A client can be configured not to check a server's certificate by setting
the parameter verify to `off'. If the server's certificate is signed by
a trusted CA then it is checked if its hostname or IP is given in its
certificate (as a CommonName, as a DNS SubjectAltName, or as an IP Sub-
jectAltName). If any match is found then the server is authenticated.
If a subject parameter is given then it is can satisfy this test as well.
This allows DNS-independent configurations using the server's IP address
in the destination and adding its hostname as subject to authenticate the
TLS connection without having to add the IP to the X.509 certificate.
If no CA is used or no trust path between CA and server certificate
exists, then hash value of the server's certificate is compared with the
hash given in fingerprint and the hash of the certificate in cert. If
the hashes are equal then the server is authenticated.
If using a CA and the client's certificate is signed by it then the
client is authenticated. Otherwise the hash of the client's certificate
is compared with the hashes given in tls_allow_fingerprints and the
hashes of the certificates given in tls_allow_clientcerts. On any match
the client is authenticated.
syslogd(8) is able to buffer temporary not writable messages in memory.
To limit the memory consumed for this buffering the following options may
The maximum number of messages buffered for one destination of type tls,
file, or pipe respectively. Defaults are `1024', `1024', and `-1' (no
The maximum memory usage in bytes of messages buffered for one destina-
tion. Defaults are `1M', `1M', and `16M'.
syslogd(8) is able to digitally sign all processed messages. The used
protocol is defined by RFC 5848 (syslog-sign): at the start of a session
the signing sender sends so called certificate blocks containing its pub-
lic key; after that it periodically sends a signed message containing
hashes of previous messages.
To detect later manipulation one has to keep a copy of the key used for
signing (otherwise an attacker could alter the logs and sign them with
his own key). If TLS is used with a DSA key then the same key will be
used for signing. This is the recommended setup because it makes it easy
to have copies of the certificate (with the public key) in backups. Oth-
erwise new keys are generated on every restart and for certain verifica-
tion it is necessary to have copies of all used keys. So logging only to
a local file is not secure; at least the used keys should be logged to
Enables signing. Set this option to enable syslog-sign and select how to
assign messages to signature groups (subsets of messages that are signed
together). To enable later signature verification and detection of lost
messages the assignment should be chosen such that all messages of one
signature group are written to the same file. Four possible values for
this option are:
0 Use one global signature group for all messages.
1 Use one signature group per priority.
2 Use signature groups for ranges of priorities.
3 Use one signature group per destination. This is a custom
strategy not defined by the standard. With this setting
one signature group is set up for every file and network
This option is only evaluated with `sign_sg=2' and allows to configure
the priority ranges for signature groups. The parameters are numerical
values used as the maximum priority for one group. The default is to use
one signature groups per facility, which is equal to setting
`sign_delim_sg2=7 15 23 31 39 ...'.
/etc/syslog.conf The syslogd(8) configuration file.
Example script to verify message signatures. (Requires
Perl and modules not part of NetBSD.)
A configuration file might appear as follows:
# Log all kernel messages, authentication messages of
# level notice or higher and anything of level err or
# higher to the console.
# Don't log private authentication messages!
# Log anything (except mail) of level info or higher.
# Don't log private authentication messages!
# Log daemon messages at debug level only
# The authpriv file has restricted access.
# Write logs with priority for later verification with syslog-sign.
# Log all the mail messages in one place.
# Everybody gets emergency messages, plus log them on another
# Log all messages of level info or higher to another
# machine using TLS with an alternative portname and a
# fingerprint for authentication
# Root and Eric get alert and higher messages.
# Save mail and news errors of level err and higher in a
# special file.
# Pipe all authentication messages to a filter.
auth.* |exec /usr/local/sbin/authfilter
# Log kernel messages to a separate file without syncing each message.
# Save ftpd transactions along with mail and news.
# Send all error messages from a RAID array through a filter.
kern.err |exec /usr/local/sbin/raidfilter
# Save pppd messages from dialhost to a separate file.
# Save non-local log messages from all programs to a separate file.
# Generate digital signatures for all messages
# to each file or network destination.
The syslog.conf file appeared in 4.3BSD, along with syslogd(8).
The effects of multiple selectors are sometimes not intuitive. For exam-
ple ``mail.crit;*.err'' will select ``mail'' facility messages at the
level of ``err'' or higher, not at the level of ``crit'' or higher.
NetBSD 10.99 November 9, 2013 NetBSD 10.99