Provided by: snort_2.9.20-0+deb11u1ubuntu1_amd64 
NAME
Snort - open source network intrusion detection system
SYNOPSIS
snort [-bCdDeEfHIMNOpqQsTUvVwWxXy?] [-A alert-mode ] [-B address-conversion-mask ] [-c rules-file ] [-F
bpf-file ] [-g group-name ] [-G id ] [-h home-net ] [-i interface ] [-k checksum-mode ] [-K logging-mode
] [-l log-dir ] [-L bin-log-file ] [-m umask ] [-n packet-count ] [-P snap-length ] [-r tcpdump-file ]
[-R name ] [-S variable=value ] [-t chroot_directory ] [-u user-name ] [-Z pathname ] [--logid id ]
[--perfmon-file pathname ] [--pid-path pathname ] [--snaplen snap-length ] [--help ] [--version ]
[--dynamic-engine-lib file ] [--dynamic-engine-lib-dir directory ] [--dynamic-detection-lib file ]
[--dynamic-detection-lib-dir directory ] [--dump-dynamic-rules directory ] [--dynamic-preprocessor-lib
file ] [--dynamic-preprocessor-lib-dir directory ] [--dynamic-output-lib file ] [--dynamic-output-lib-dir
directory ] [--alert-before-pass ] [--treat-drop-as-alert ] [--treat-drop-as-ignore ] [--process-all-
events ] [--enable-inline-test ] [--create-pidfile ] [--nolock-pidfile ] [--no-interface-pidfile ]
[--disable-attribute-reload-thread ] [--pcap-single= tcpdump-file ] [--pcap-filter= filter ] [--pcap-
list= list ] [--pcap-dir= directory ] [--pcap-file= file ] [--pcap-no-filter ] [--pcap-reset ] [--pcap-
reload ] [--pcap-show ] [--exit-check count ] [--conf-error-out ] [--enable-mpls-multicast ] [--enable-
mpls-overlapping-ip ] [--max-mpls-labelchain-len ] [--mpls-payload-type ] [--require-rule-sid ] [--daq
type ] [--daq-mode mode ] [--daq-var name=value ] [--daq-dir dir ] [--daq-list [dir] ] [--dirty-pig ]
[--cs-dir dir ] [--ha-peer ] [--ha-out file ] [--ha-in file ] expression
DESCRIPTION
Snort is an open source network intrusion detection system, capable of performing real-time traffic
analysis and packet logging on IP networks. It can perform protocol analysis, content searching/matching
and can be used to detect a variety of attacks and probes, such as buffer overflows, stealth port scans,
CGI attacks, SMB probes, OS fingerprinting attempts, and much more. Snort uses a flexible rules language
to describe traffic that it should collect or pass, as well as a detection engine that utilizes a modular
plugin architecture. Snort also has a modular real-time alerting capability, incorporating alerting and
logging plugins for syslog, a ASCII text files, UNIX sockets or XML.
Snort has three primary uses. It can be used as a straight packet sniffer like tcpdump(1), a packet
logger (useful for network traffic debugging, etc), or as a full blown network intrusion detection
system.
Snort logs packets in tcpdump(1) binary format or in Snort's decoded ASCII format to a hierarchy of
logging directories that are named based on the IP address of the "foreign" host.
OPTIONS
-A alert-mode
Alert using the specified alert-mode. Valid alert modes include fast, full, none, and unsock.
Fast writes alerts to the default "alert" file in a single-line, syslog style alert message. Full
writes the alert to the "alert" file with the full decoded header as well as the alert message.
None turns off alerting. Unsock is an experimental mode that sends the alert information out over
a UNIX socket to another process that attaches to that socket.
-b Log packets in a tcpdump(1) formatted file. All packets are logged in their native binary state
to a tcpdump formatted log file named with the snort start timestamp and "snort.log". This option
results in much faster operation of the program
since it doesn't have to spend time in the packet binary->text converters. Snort can keep up
pretty well with 100Mbps networks in '-b' mode. To choose an alternate name for the binary log
file, use the '-L' switch.
-B address-conversion-mask
Convert all IP addresses in home-net to addresses specified by address-conversion-mask. Used to
obfuscate IP addresses within binary logs. Specify home-net with the '-h' switch. Note this is
not the same as $HOME_NET.
-c config-file
Use the rules located in file config-file.
-C Print the character data from the packet payload only (no hex).
-d Dump the application layer data when displaying packets in verbose or packet logging mode.
-D Run Snort in daemon mode. Alerts are sent to /var/log/snort/alert unless otherwise specified.
-e Display/log the link layer packet headers.
-E *WIN32 ONLY* Log alerts to the Windows Event Log.
-f Activate PCAP line buffering
-F bpf-file
Read BPF filters from bpf-file. This is handy for people running Snort as a SHADOW replacement or
with a love Of super complex BPF filters. See the "expressions" section of this man page for more
info on writing BPF filters.
-g group
Change the group/GID Snort runs under to group after initialization. This switch allows Snort to
drop root privileges after it's initialization phase has completed as a security measure.
-G id Use id as a base event ID when logging events.
-h home-net
Set the "home network" to home-net. The format of this address variable is a network prefix plus
a CIDR block, such as 192.168.1.0/24. Once this variable is set, all decoded packet logging will
be done relative to the home network address space. This is useful because of the way that Snort
formats its ASCII log data. With this value set to the local network, all decoded output will be
logged into decode directories with the address of the foreign computer as the directory name,
which is very useful during traffic analysis. This option does not change "$HOME_NET" in IDS mode.
-H Force hash tables to be deterministic instead of using a random number generator for the seed &
scale. Useful for testing and generating repeatable results with the same traffic.
-i interface
Sniff packets on interface.
-I Print out the receiving interface name in alerts.
-k checksum-mode
Tune the internal checksum verification functionality with alert-mode. Valid checksum modes
include all, noip, notcp, noudp, noicmp, and none. All activates checksum verification for all
supported protocols. Noip turns off IP checksum verification, which is handy if the gateway
router is already dropping packets that fail their IP checksum checks. Notcp turns off TCP
checksum verification, all other checksum modes are on. noudp turns off UDP checksum
verification. Noicmp turns off ICMP checksum verification. None turns off the entire checksum
verification subsystem.
-K logging-mode
Select a packet logging mode. The default is pcap. logging-mode. Valid logging modes include
pcap, ascii, and none. Pcap logs packets through the pcap library into pcap (tcpdump) format.
Ascii logs packets in the old "directories and files" format with packet printouts in each file.
None Turns off packet logging.
-l log-dir
Set the output logging directory to log-dir. All plain text alerts and packet logs go into this
directory. If this option is not specified, the default logging directory is set to
/var/log/snort.
-L binary-log-file
Set the filename of the binary log file to binary-log-file. If this switch is not used, the
default name is a timestamp for the time that the file is created plus "snort.log".
-m umask
Set the file mode creation mask to umask
-M Log console messages to syslog when not running daemon mode. Using both -D and -M will send all
messages to syslog including e.g. SIGUSR1 dump packet stats. This switch has no impact on logging
of alerts.
-n packet-count
Process packet-count packets and exit.
-N Turn off packet logging. The program still generates alerts normally.
-O Obfuscate the IP addresses when in ASCII packet dump mode. This switch changes the IP addresses
that get printed to the screen/log file to "xxx.xxx.xxx.xxx". If the homenet address switch is
set (-h), only addresses on the homenet will be obfuscated while non- homenet IPs will be left
visible. Perfect for posting to your favorite security mailing list!
-p Turn off promiscuous mode sniffing.
-P snap-length
Set the packet snaplen to snap-length. By default, this is set to 1514.
-q Quiet operation. Don't display banner and initialization information. In daemon mode, banner and
initialization information is not logged to syslog.
-Q Enable inline mode operation.
-r tcpdump-file
Read the tcpdump-formatted file tcpdump-file. This will cause Snort to read and process the file
fed to it. This is useful if, for instance, you've got a bunch of SHADOW files that you want to
process for content, or even if you've got a bunch of reassembled packet fragments which have been
written into a tcpdump formatted file.
-R name
Use name as a suffix to the snort pidfile.
-s Send alert messages to syslog. On linux boxen, they will appear in /var/log/secure,
/var/log/messages on many other platforms.
-S variable=value
Set variable name "variable" to value "value". This is useful for setting the value of a defined
variable name in a Snort rules file to a command line specified value. For instance, if you
define a HOME_NET variable name inside of a Snort rules file, you can set this value from it's
predefined value at the command line.
-t chroot
Changes Snort's root directory to chroot after initialization. Please note that all log/alert
filenames are relative to the chroot directory if chroot is used.
-T Snort will start up in self-test mode, checking all the supplied command line switches and rules
files that are handed to it and indicating that everything is ready to proceed. This is a good
switch to use if daemon mode is going to be used, it verifies that the Snort configuration that is
about to be used is valid and won't fail at run time. Note, Snort looks for either /etc/snort.conf
or ./snort.conf. If your config lives elsewhere, use the -c option to specify a valid config-
file.
-u user
Change the user/UID Snort runs under to user after initialization.
-U Changes the timestamp in all logs to be in UTC
-v Be verbose. Prints packets out to the console. There is one big problem with verbose mode: it's
slow. If you are doing IDS work with Snort, don't use the '-v' switch, you WILL drop packets.
-V Show the version number and exit.
-w Show management frames if running on an 802.11 (wireless) network.
-W *WIN32 ONLY* Enumerate the network interfaces available.
-x Exit if Snort configuration problems occur such as duplicate gid/sid or flowbits without Stream5.
-X Dump the raw packet data starting at the link layer. This switch overrides the '-d' switch.
-y Include the year in alert and log files
-Z pathname
Set the perfmonitor preprocessor path/filename to pathname.
-? Show the program usage statement and exit.
--logid id
Same as -G.
--perfmon-file pathname
Same as -Z.
--pid-path directory
Specify the directory for the Snort PID file.
--snaplen snap-length
Same as -P.
--help Same as -?
--version
Same as -V
--dynamic-engine-lib file
Load a dynamic detection engine shared library specified by file.
--dynamic-engine-lib-dir directory
Load all dynamic detection engine shared libraries specified from directory.
--dynamic-detection-lib file
Load a dynamic detection rules shared library specified by file.
--dynamic-detection-lib-dir directory
Load all dynamic detection rules shared libraries specified from directory.
--dump-dynamic-rules directory
Create stub rule files from all loaded dynamic detection rules libraries. Files will be created
in directory. This is required to be done prior to running snort using those detection rules and
the generated rules files must be included in snort.conf.
--dynamic-preprocessor-lib file
Load a dynamic preprocessor shared library specified by file.
--dynamic-preprocessor-lib-dir directory
Load all dynamic preprocessor shared libraries specified from directory.
--alert-before-pass
Process alert, drop, sdrop, or reject before pass. Default is pass before alert, drop, etc.
--treat-drop-as-alert
Converts drop, sdrop, and reject rules into alert rules during startup.
--treat-drop-as-ignore
Use drop, sdrop, and reject rules to ignore session traffic when not inline.
--process-all-events
Process all triggered events in group order, per Rule Ordering configuration. Default stops after
first group.
--enable-inline-test
Enable Inline-Test Mode Operation.
--pid-path directory
Specify the path for Snort's PID file.
--create-pidfile
Create PID file, even when not in Daemon mode.
--nolock-pidfile
Do not try to lock Snort PID file.
--no-interface-pidfile
Do not include the interface name in Snort PID file
--pcap-single=tcpdump-file
Same as -r. Added for completeness.
--pcap-filter=filter
Shell style filter to apply when getting pcaps from file or directory. This filter will apply to
any --pcap-file or --pcap-dir arguments following. Use --pcap-no-filter to delete filter for
following --pcap-file or --pcap-dir arguments or specify --pcap-filter again to forget previous
filter and to apply to following --pcap-file or --pcap-dir arguments.
--pcap-list="list"
A space separated list of pcaps to read.
--pcap-dir=directory
A directory to recurse to look for pcaps. Sorted in ascii order.
--pcap-file=file
File that contains a list of pcaps to read. Can specify path to pcap or directory to recurse to
get pcaps.
--pcap-no-filter
Reset to use no filter when getting pcaps from file or directory.
--pcap-reset
If reading multiple pcaps, reset snort to post-configuration state before reading next pcap. The
default, i.e. without this option, is not to reset state.
--pcap-show
Print a line saying what pcap is currently being read.
--exit-check=count
Signal termination after <count> callbacks from DAQ_Acquire(), showing the time it takes from
signaling until DAQ_Stop() is called.
--conf-error-out
Same as -x.
--require-rule-sid
Require an SID for every rule to be correctly threshold all rules.
--daq <type>
Select packet acquisition module (default is pcap).
--daq-mode <mode>
Select the DAQ operating mode.
--daq-var <name=value>
Specify extra DAQ configuration variable.
--daq-dir <dir>
Tell Snort where to find desired DAQ.
--daq-list [<dir>]
List packet acquisition modules available in dir.
--cs-dir <dir>
Tell Snort to use control socket and create the socket in dir.
expression
selects which packets will be dumped. If no expression is given, all packets on the net will be
dumped. Otherwise, only packets for which expression is `true' will be dumped.
The expression consists of one or more primitives. Primitives usually consist of an id (name or
number) preceded by one or more qualifiers. There are three different kinds of qualifier:
type qualifiers say what kind of thing the id name or number refers to. Possible types are
host, net and port. E.g., `host foo', `net 128.3', `port 20'. If there is no type
qualifier, host is assumed.
dir qualifiers specify a particular transfer direction to and/or from id. Possible directions
are src, dst, src or dst and src and dst. E.g., `src foo', `dst net 128.3', `src or dst
port ftp-data'. If there is no dir qualifier, src or dst is assumed. For `null' link
layers (i.e. point to point protocols such as slip) the inbound and outbound qualifiers can
be used to specify a desired direction.
proto qualifiers restrict the match to a particular protocol. Possible protos are: ether, fddi,
ip, arp, rarp, decnet, lat, sca, moprc, mopdl, tcp and udp. E.g., `ether src foo', `arp
net 128.3', `tcp port 21'. If there is no proto qualifier, all protocols consistent with
the type are assumed. E.g., `src foo' means `(ip or arp or rarp) src foo' (except the
latter is not legal syntax), `net bar' means `(ip or arp or rarp) net bar' and `port 53'
means `(tcp or udp) port 53'.
[`fddi' is actually an alias for `ether'; the parser treats them identically as meaning ``the data
link level used on the specified network interface.'' FDDI headers contain Ethernet-like source
and destination addresses, and often contain Ethernet-like packet types, so you can filter on
these FDDI fields just as with the analogous Ethernet fields. FDDI headers also contain other
fields, but you cannot name them explicitly in a filter expression.]
In addition to the above, there are some special `primitive' keywords that don't follow the
pattern: gateway, broadcast, less, greater and arithmetic expressions. All of these are described
below.
More complex filter expressions are built up by using the words and, or and not to combine
primitives. E.g., `host foo and not port ftp and not port ftp-data'. To save typing, identical
qualifier lists can be omitted. E.g., `tcp dst port ftp or ftp-data or domain' is exactly the
same as `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
Allowable primitives are:
dst host host
True if the IP destination field of the packet is host, which may be either an address or a
name.
src host host
True if the IP source field of the packet is host.
host host
True if either the IP source or destination of the packet is host. Any of the above host
expressions can be prepended with the keywords, ip, arp, or rarp as in:
ip host host
which is equivalent to:
ether proto \ip and host host
If host is a name with multiple IP addresses, each address will be checked for a match.
ether dst ehost
True if the ethernet destination address is ehost. Ehost may be either a name from
/etc/ethers or a number (see ethers(3N) for numeric format).
ether src ehost
True if the ethernet source address is ehost.
ether host ehost
True if either the ethernet source or destination address is ehost.
gateway host
True if the packet used host as a gateway. I.e., the ethernet source or destination
address was host but neither the IP source nor the IP destination was host. Host must be a
name and must be found in both /etc/hosts and /etc/ethers. (An equivalent expression is
ether host ehost and not host host
which can be used with either names or numbers for host / ehost.)
dst net net
True if the IP destination address of the packet has a network number of net. Net may be
either a name from /etc/networks or a network number (see networks(4) for details).
src net net
True if the IP source address of the packet has a network number of net.
net net
True if either the IP source or destination address of the packet has a network number of
net.
net net mask mask
True if the IP address matches net with the specific netmask. May be qualified with src or
dst.
net net/len
True if the IP address matches net a netmask len bits wide. May be qualified with src or
dst.
dst port port
True if the packet is ip/tcp or ip/udp and has a destination port value of port. The port
can be a number or a name used in /etc/services (see tcp(4P) and udp(4P)). If a name is
used, both the port number and protocol are checked. If a number or ambiguous name is
used, only the port number is checked (e.g., dst port 513 will print both tcp/login traffic
and udp/who traffic, and port domain will print both tcp/domain and udp/domain traffic).
src port port
True if the packet has a source port value of port.
port port
True if either the source or destination port of the packet is port. Any of the above port
expressions can be prepended with the keywords, tcp or udp, as in:
tcp src port port
which matches only tcp packets whose source port is port.
less length
True if the packet has a length less than or equal to length. This is equivalent to:
len <= length.
greater length
True if the packet has a length greater than or equal to length. This is equivalent to:
len >= length.
ip proto protocol
True if the packet is an ip packet (see ip(4P)) of protocol type protocol. Protocol can be
a number or one of the names icmp, igrp, udp, nd, or tcp. Note that the identifiers tcp,
udp, and icmp are also keywords and must be escaped via backslash (\), which is \\ in the
C-shell.
ether broadcast
True if the packet is an ethernet broadcast packet. The ether keyword is optional.
ip broadcast
True if the packet is an IP broadcast packet. It checks for both the all-zeroes and all-
ones broadcast conventions, and looks up the local subnet mask.
ether multicast
True if the packet is an ethernet multicast packet. The ether keyword is optional. This
is shorthand for `ether[0] & 1 != 0'.
ip multicast
True if the packet is an IP multicast packet.
ether proto protocol
True if the packet is of ether type protocol. Protocol can be a number or a name like ip,
arp, or rarp. Note these identifiers are also keywords and must be escaped via backslash
(\). [In the case of FDDI (e.g., `fddi protocol arp'), the protocol identification comes
from the 802.2 Logical Link Control (LLC) header, which is usually layered on top of the
FDDI header. Tcpdump assumes, when filtering on the protocol identifier, that all FDDI
packets include an LLC header, and that the LLC header is in so-called SNAP format.]
decnet src host
True if the DECNET source address is host, which may be an address of the form ``10.123'',
or a DECNET host name. [DECNET host name support is only available on Ultrix systems that
are configured to run DECNET.]
decnet dst host
True if the DECNET destination address is host.
decnet host host
True if either the DECNET source or destination address is host.
ip, arp, rarp, decnet
Abbreviations for:
ether proto p
where p is one of the above protocols.
lat, moprc, mopdl
Abbreviations for:
ether proto p
where p is one of the above protocols. Note that Snort does not currently know how to
parse these protocols.
tcp, udp, icmp
Abbreviations for:
ip proto p
where p is one of the above protocols.
expr relop expr
True if the relation holds, where relop is one of >, <, >=, <=, =, !=, and expr is an
arithmetic expression composed of integer constants (expressed in standard C syntax), the
normal binary operators [+, -, *, /, &, |], a length operator, and special packet data
accessors. To access data inside the packet, use the following syntax:
proto [ expr : size ]
Proto is one of ether, fddi, ip, arp, rarp, tcp, udp, or icmp, and indicates the protocol
layer for the index operation. The byte offset, relative to the indicated protocol layer,
is given by expr. Size is optional and indicates the number of bytes in the field of
interest; it can be either one, two, or four, and defaults to one. The length operator,
indicated by the keyword len, gives the length of the packet.
For example, `ether[0] & 1 != 0' catches all multicast traffic. The expression `ip[0] &
0xf != 5' catches all IP packets with options. The expression `ip[6:2] & 0x1fff = 0'
catches only unfragmented datagrams and frag zero of fragmented datagrams. This check is
implicitly applied to the tcp and udp index operations. For instance, tcp[0] always means
the first byte of the TCP header, and never means the first byte of an intervening
fragment.
Primitives may be combined using:
A parenthesized group of primitives and operators (parentheses are special to the Shell and
must be escaped).
Negation (`!' or `not').
Concatenation (`&&' or `and').
Alternation (`||' or `or').
Negation has highest precedence. Alternation and concatenation have equal precedence and
associate left to right. Note that explicit and tokens, not juxtaposition, are now required for
concatenation.
If an identifier is given without a keyword, the most recent keyword is assumed. For example,
not host vs and ace
is short for
not host vs and host ace
which should not be confused with
not ( host vs or ace )
Expression arguments can be passed to Snort as either a single argument or as multiple arguments,
whichever is more convenient. Generally, if the expression contains Shell metacharacters, it is
easier to pass it as a single, quoted argument. Multiple arguments are concatenated with spaces
before being parsed.
READING PCAPS
Instead of having Snort listen on an interface, you can give it a packet capture to read. Snort will
read and analyze the packets as if they came off the wire. This can be useful for testing and debugging
Snort.
Read a single pcap
$ snort -r foo.pcap
$ snort --pcap-single=foo.pcap
Read pcaps from a file
$ cat foo.txt
foo1.pcap
foo2.pcap
/home/foo/pcaps
$ snort --pcap-file=foo.txt
This will read foo1.pcap, foo2.pcap and all files under /home/foo/pcaps. Note that Snort will not
try to determine whether the files under that directory are really pcap files or not.
Read pcaps from a command line list
$ snort --pcap-list="foo1.pcap foo2.pcap foo3.pcap"
This will read foo1.pcap, foo2.pcap and foo3.pcap.
Read pcaps under a directory
$ snort --pcap-dir="/home/foo/pcaps"
This will include all of the files under /home/foo/pcaps.
Using filters
$ cat foo.txt
foo1.pcap
foo2.pcap
/home/foo/pcaps
$ snort --pcap-filter="*.pcap" --pcap-file=foo.txt
$ snort --pcap-filter="*.pcap" --pcap-dir=/home/foo/pcaps
The above will only include files that match the shell pattern "*.pcap", in other words, any file
ending in ".pcap".
$ snort --pcap-filter="*.pcap --pcap-file=foo.txt \
> --pcap-filter="*.cap" --pcap-dir=/home/foo/pcaps
In the above, the first filter "*.pcap" will only be applied to the pcaps in the file "foo.txt" (and
any directories that are recursed in that file). The addition of the second filter "*.cap" will
cause the first filter to be forgotten and then applied to the directory /home/foo/pcaps, so only
files ending in ".cap" will be included from that directory.
$ snort --pcap-filter="*.pcap --pcap-file=foo.txt \
> --pcap-no-filter --pcap-dir=/home/foo/pcaps
In this example, the first filter will be applied to foo.txt, then no filter will be applied to the
files found under /home/foo/pcaps, so all files found under /home/foo/pcaps will be included.
$ snort --pcap-filter="*.pcap --pcap-file=foo.txt \
> --pcap-no-filter --pcap-dir=/home/foo/pcaps \
> --pcap-filter="*.cap" --pcap-dir=/home/foo/pcaps2
In this example, the first filter will be applied to foo.txt, then no filter will be applied to the
files found under /home/foo/pcaps, so all files found under /home/foo/pcaps will be included, then
the filter "*.cap" will be applied to files found under /home/foo/pcaps2.
Resetting state
$ snort --pcap-dir=/home/foo/pcaps --pcap-reset
The above example will read all of the files under /home/foo/pcaps, but after each pcap is read,
Snort will be reset to a post-configuration state, meaning all buffers will be flushed, statistics
reset, etc. For each pcap, it will be like Snort is seeing traffic for the first time.
Printing the pcap
$ snort --pcap-dir=/home/foo/pcaps --pcap-show
The above example will read all of the files under /home/foo/pcaps and will print a line indicating
which pcap is currently being read.
RULES
Snort uses a simple but flexible rules language to describe network packet signatures and associate them
with actions. The current rules document can be found at http://www.snort.org/snort-rules.
NOTES
The following signals have the specified effect when sent to the daemon process using the kill(1)
command:
SIGHUP Causes the daemon to close all opened files and restart. Please note that this will only work if
the full pathname is used to invoke snort in daemon mode, otherwise snort will just exit with an
error message being sent to syslogd(8).
SIGUSR1
Causes the program to dump its current packet statistical information to the console or syslogd(8)
if in daemon mode.
SIGUSR2
Causes the program to rotate Perfmonitor statistical information to the console or syslogd(8) if
in daemon mode.
SIGURG Causes the program to reload attribute table.
SIGCHLD
Used internally.
Please refer to manual for more details. Any other signal might cause the daemon to close all opened
files and exit.
CONFIGURATION
In Debian, there are several ways in which Snort can be configured. The configuration file
/etc/snort/snort.conf provides the configuration for the software itself. Users can customise this
configuration. In systems which have multiple interfaces, it is possible to have a different Snort
instance per network interface and adjust the specific configuration for one interface using
/etc/snort/snort.INTERFACE.conf (where INTERFACE should be replaced by the interface name).
There are additional configuration files in /etc/snort which modify Snort behaviour. These include:
attribute_table.dtd, file_magic.conf, threshold.conf and unicode.map
In addition, Debian provides a specific configuration file to manage the startup of Snort through the
/etc/snort/snort.debian.conf configuration file. This file is modified by the packaging system, using
debconf, and defines whether Snort is to be started up on system boot or manually, defines specific
options for the Snort daemon when it is started and sets values to be used by the snort-stat cron script
(if enabled).
Finally, the configuration file /etc/default/snort is used to define parameters which are applicable to
the Snort startup (init.d) script. These include: daemon startup parameters, user and group Snort will
run as, log directory and whether to run Snort when the interfaces to be monitored are not available.
LOGS AND ALERTS
In Debian, the Snort logs are available under /var/log/snort/ and includes /var/log/snort/snort.log,
/var/log/snort/snort.alert and /var/log/snort/snort.alert.fast
The first two of these logs are saved using the unified format which can be read using the u2spewfoo
tool. For more information read /usr/share/doc/snort/README.unified2 which is provided by the snort-doc
package. The log files in unified2 format can also be converted to other formats (currently only pcap is
supported) using the u2boat tool. The last log file (snort.alert.fast) is a one line format that provides
fast alerts. These alerts are read by the snort-stat and sent by email to a designed administrator if
eneabled in the Debian package configuration.
The location of the log directory can be adjusted through the configuration of the LOGDIR parameter in
the /etc/default/snort configuration file.
The log file /var/log/snort/snort.log contains the packets logged, while the /var/log/snort/snort.alert
contains only the alerts generated.
In addition to this, all alerts are logged into syslog using LOG_AUTH and LOG_ALERT.
The logging and alerting mode can be modified by configuring the /etc/snort/snort.conf file.
HISTORY
Snort has been freely available under the GPL license since 1998.
DIAGNOSTICS
Snort returns a 0 on a successful exit, 1 if it exits on an error.
BUGS
After consulting the BUGS file included with the source distributon and available in Debian systems in
/usr/share/doc/BUGS, as well as the Debian-specific bugs published in https://bugs.debian.org/cgi-
bin/pkgreport.cgi?package=snort please send bug reports to Debian using the reportbug program. For more
information about reporting bugs in Debian please read https://www.debian.org/Bugs/Reporting
If you believe the bug lies with the upstream package, please send bug reports directly to snort-
devel@lists.snort.org
AUTHOR
The main author of Snort is Martin Roesch <roesch@snort.org>
In addition, many people have contributed to Snort development. For a full list please read
/usr/share/doc/snort/CREDITS.gz
This Debian package was created by Christian Hammers <ch@debian.org> (from 1999 to 2001), Robert van der
Meulen <rvdm@debian.org> (2001 to 2002), Sander Smeenk <ssmeenk@debian.org> (2002 to 2004) and Javier
Fernández-Sanguino <jfs@debian.org> (2004 to 2020). It includes with contributions from many different
Debian developers and users. All of them are credited in the Debian changelog file which can be found at
/usr/share/doc/snort/changelog.Debian.gz and /usr/share/doc/snort/copyright
SEE ALSO
tcpdump(1), pcap(3), u2boat(8), u2spewfoo(8), snort-stat(8)
December 2011 SNORT(8)