PFLOGD(8) | System Manager's Manual | PFLOGD(8)

# NAME

`pflogd` — packet filter logging daemon

# SYNOPSIS

`pflogd` | [`-Dx`] [`-d` delay] [`-f` filename] [`-i` interface] [`-s` snaplen] [expression ...]

# DESCRIPTION

`pflogd` is a background daemon which reads packets logged by pf(4) to a pflog(4) interface, normally pflog0, and writes the packets to a logfile (normally /var/log/pflog) in tcpdump(8) binary format. These logs can be reviewed later using the `-r` option of tcpdump(8), hopefully offline in case there are bugs in the packet parsing code of tcpdump(8).

`pflogd` closes and then re-opens the log file when it receives `SIGHUP`, permitting newsyslog(8) to rotate logfiles automatically. `SIGALRM` causes `pflogd` to flush the current logfile buffers to the disk, thus making the most recent logs available. The buffers are also flushed every delay seconds.

If the log file contains data after a restart or a `SIGHUP`, new logs are appended to the existing file. If the existing log file was created with a different snaplen, `pflogd` temporarily uses the old snaplen to keep the log file consistent.

`pflogd` tries to preserve the integrity of the log file against I/O errors. Furthermore, integrity of an existing log file is verified before appending. If there is an invalid log file or an I/O error, logging is suspended until a `SIGHUP` or a `SIGALRM` is received.

The options are as follows:

`-D`
  Debugging mode. `pflogd` does not disassociate from the controlling terminal.
`-d` delay
  Time in seconds to delay between automatic flushes of the file. This may be specified with a value between 5 and 3600 seconds. If not specified, the default is 60 seconds.
`-f` filename
  Log output filename. Default is /var/log/pflog.
`-i` interface
  Specifies the pflog(4) interface to use. By default, `pflogd` will use pflog0.
`-s` snaplen
  Analyze at most the first snaplen bytes of data from each packet rather than the default of 160. The default of 160 is adequate for IP, ICMP, TCP, and UDP headers but may truncate protocol information for other protocols. Other file parsers may desire a higher snaplen.
`-x`
  Check the integrity of an existing log file, and return.
expression
  Selects which packets will be dumped, using the regular language of tcpdump(8). Tcpdump has been extended to be able to filter on the pfloghdr structure defined in `<net/if_pflog.h>`. It can restrict the output to packets logged on a specified interface, a rule number, a reason, a direction, an IP family or an action.

  ip
    Address family equals IPv4.
  ip6
    Address family equals IPv6.
  ifname kue0
    Interface name equals "kue0".
  on kue0
    Interface name equals "kue0".
  ruleset authpf
    Ruleset name equals "authpf".
  rulenum 10
    Rule number equals 10.
  reason match
    Reason equals match. Also accepts "bad-offset", "fragment", "short", "normalize", "memory", "bad-timestamp", "congestion", "ip-option", "proto-cksum", "state-mismatch", "state-insert", "state-limit", "src-limit", and "synproxy".
  action pass
    Action equals pass. Also accepts "block" and "match".
  inbound
    The direction was inbound.
  outbound
    The direction was outbound.

# FILES

/var/log/pflog
  Default log file.

# EXAMPLES

Log specific TCP packets to a different log file with a large snaplen (useful with a "log all" rule to dump complete sessions):

    # pflogd -s 1600 -f suspicious.log port 80 and host evilhost

Log from another pflog(4) interface, excluding specific packets:

    # pflogd -i pflog3 -f network3.log "not (tcp and port 23)"

Display binary logs:

    # tcpdump -n -e -ttt -r /var/log/pflog

Display the logs in real time (this does not interfere with the operation of `pflogd`):

    # tcpdump -n -e -ttt -i pflog0

Display the logs in real time of inbound packets that were blocked on the wi0 interface:

    # tcpdump -n -e -ttt -i pflog0 inbound and action block and on wi0

# SEE ALSO

pcap_open_live(3), pf(4), pflog(4), pf.conf(5), newsyslog(8), tcpdump(8)

# HISTORY

The `pflogd` command appeared in OpenBSD 3.0.

# AUTHORS

`pflogd` was written by Can Erkin Acar <canacar@openbsd.org>.

May 16, 2025 | Debian