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SNMPD(8) Net-SNMP SNMPD(8)

NAME
snmpd - daemon to respond to SNMP request packets.

SYNOPSIS
snmpd [OPTIONS] [LISTENING ADDRESSES]

DESCRIPTION
snmpd is an SNMP agent which binds to a port and awaits requests from SNMP management software. Upon receiving a
request, it processes the request(s), collects the requested information and/or performs the requested operation(s) and
returns the information to the sender.

OPTIONS
-a Log the source addresses of incoming requests.

-A Append to the log file rather than truncating it.

-c FILE Read FILE as a configuration file (or a comma-separated list of configuration files). Note that the loaded file
will only understand snmpd.conf tokens, unless the configuration type is specified in the file as described in
the snmp_config man page under SWITCHING CONFIGURATION TYPES IN MID-FILE.

-C Do not read any configuration files except the ones optionally specified by the -c option. Note that this behav-
iour also covers the persistent configuration files. This may result in dynamically-assigned values being reset
following an agent restart, unless the relevant persistent config files are explicitly loaded using the -c
option.

-d Dump (in hexadecimal) the sent and received SNMP packets.

-D[TOKEN[,...]]
Turn on debugging output for the given TOKEN(s). Without any tokens specified, it defaults to printing all the
tokens (which is equivalent to the keyword "ALL"). You might want to try ALL for extremely verbose output.
Note: You can not put a space between the -D flag and the listed TOKENs.

-f Do not fork() from the calling shell.

-g GID Change to the numerical group ID GID after opening listening sockets.

-h, --help
Display a brief usage message and then exit.

-H Display a list of configuration file directives understood by the agent and then exit.

-I [-]INITLIST
Specifies which modules should (or should not) be initialized when the agent starts up. If the comma-separated
INITLIST is preceded with a '-', it is the list of modules that should not be started. Otherwise this is the
list of the only modules that should be started.

To get a list of compiled modules, run the agent with the arguments -Dmib_init -H (assuming debugging support has
been compiled in).

-L[efos]
Specify where logging output should be directed (standard error or output, to a file or via syslog). See LOGGING
OPTIONS in snmpcmd(5) for details.

-m MIBLIST
Specifies a colon separated list of MIB modules to load for this application. This overrides the environment
variable MIBS. See snmpcmd(1) for details.

-M DIRLIST
Specifies a colon separated list of directories to search for MIBs. This overrides the environment variable MIB-
DIRS. See snmpcmd(1) for details.

-n NAME Set an alternative application name (which will affect the configuration files loaded). By default this will be
snmpd, regardless of the name of the actual binary.

-p FILE Save the process ID of the daemon in FILE.

-q Print simpler output for easier automated parsing.

-r Do not require root access to run the daemon. Specifically, do not exit if files only accessible to root (such
as /dev/kmem etc.) cannot be opened.

-u UID Change to the user ID UID (which can be given in numerical or textual form) after opening listening sockets.

-U Instructs the agent to not remove its pid file (see the -p option) on shutdown. Overrides the leave_pidfile token
in the snmpd.conf file, see snmpd.conf(5).

-v, --version
Print version information for the agent and then exit.

-V Symbolically dump SNMP transactions.

-x ADDRESS
Listens for AgentX connections on the specified address rather than the default "/var/agentx/master". The
address can either be a Unix domain socket path, or the address of a network interface. The format is the same
as the format of listening addresses described below.

-X Run as an AgentX subagent rather than as an SNMP master agent.

--name="value"
Allows to specify any token ("name") supported in the snmpd.conf file and sets its value to "value". Overrides
the corresponding token in the snmpd.conf file. See snmpd.conf(5) for the full list of tokens.

LISTENING ADDRESSES
By default, snmpd listens for incoming SNMP requests on UDP port 161 on all IPv4 interfaces. However, it is possible to
modify this behaviour by specifying one or more listening addresses as arguments to snmpd. A listening address takes the
form:

[<transport-specifier>:]<transport-address>

At its simplest, a listening address may consist only of a port number, in which case snmpd listens on that UDP port on
all IPv4 interfaces. Otherwise, the <transport-address> part of the specification is parsed according to the following
table:

<transport-specifier> <transport-address> format

udp (default) hostname[:port] or IPv4-address[:port]

tcp hostname[:port] or IPv4-address[:port]

unix pathname

ipx [network]:node[/port]

aal5pvc or pvc [interface.][VPI.]VCI

udp6 or udpv6 or udpipv6 hostname[:port] or IPv6-address[:port]

tcp6 or tcpv6 or tcpipv6 hostname[:port] or IPv6-address[:port]

ssh hostname:port

dtlsudp hostname:port

Note that <transport-specifier> strings are case-insensitive so that, for example, "tcp" and "TCP" are equivalent. Here
are some examples, along with their interpretation:

127.0.0.1:161 listen on UDP port 161, but only on the loopback interface. This prevents snmpd being queried
remotely. The port specification ":161" is not strictly necessary since that is the default
SNMP port.

TCP:1161 listen on TCP port 1161 on all IPv4 interfaces.

ipx:/40000 listen on IPX port 40000 on all IPX interfaces.

unix:/tmp/local-agent listen on the Unix domain socket /tmp/local-agent.

/tmp/local-agent is identical to the previous specification, since the Unix domain is assumed if the first charac-
ter of the <transport-address> is '/'.

PVC:161 listen on the AAL5 permanent virtual circuit with VPI=0 and VCI=161 (decimal) on the first ATM
adapter in the machine.

udp6:10161 listen on port 10161 on all IPv6 interfaces.

ssh:127.0.0.1:22 Allows connections from the snmp subsystem on the ssh server on port 22. The details of using
SNMP over SSH are defined below.

dtlsudp:127.0.0.1:9161 Listen for connections over DTLS on UDP port 9161. The snmp.conf file must have the
defX509ServerPub, defX509ServerPriv, and defX509ClientCerts configuration tokens defined.

Note that not all the transport domains listed above will always be available; for instance, hosts with no IPv6 support
will not be able to use udp6 transport addresses, and attempts to do so will result in the error "Error opening specified
endpoint". Likewise, since AAL5 PVC support is only currently available on Linux, it will fail with the same error on
other platforms.

Transport Specific Notes
ssh The SSH transport, on the server side, is actually just a unix named pipe that can be connected to via a ssh sub-
system configured in the main ssh server. The pipe location (configurable with the sshtosnmpsocket token in
snmp.conf) is /var/net-snmp/sshtosnmp. Packets should be submitted to it via the sshtosnmp application, which
also sends the user ID as well when starting the connection. The TSM security model should be used when packets
should process it.

The sshtosnmp command knows how to connect to this pipe and talk to it. It should be configured in the OpenSSH
sshd configuration file (which is normally /etc/ssh/sshd_config using the following configuration line:

Subsystem snmp /usr/local/bin/sshtosnmp

The sshtosnmp command will need read/write access to the /var/net-snmp/sshtosnmp pipe. Although it should be
fairly safe to grant access to the average user since it still requires modifications to the ACM settings before
the user can perform operations, paranoid administrators may want to make the /var/net-snmp directory accessible
only by users in a particular group. Use the sshtosnmpsocketperms snmp.conf configure option to set the permis-
sions, owner and group of the created socket.

Access control can be granted to the user "foo" using the following style of simple snmpd.conf settings:

rouser -s tsm foo authpriv

Note that "authpriv" is acceptable assuming as SSH protects everything that way (assuming you have a non-insane
setup). snmpd has no notion of how SSH has actually protected a packet and thus the snmp agent assumes all pack-
ets passed through the SSH transport have been protected at the authpriv level.

dtlsudp The DTLS protocol, which is based off of TLS, requires both client and server certificates to establish the con-
nection and authenticate both sides. In order to do this, the client will need to configure the snmp.conf file
with the defX509ServerCerts, defX509ClientPriv, and defX509ClientPub configuration tokens. The server will need
to configure the snmp.conf file with the defX509ServerPub, defX509ServerPriv, and defX509ClientCerts configura-
tion tokens defined.

Access control setup is similar to the ssh transport as the TSM security model should be used to protect the
packet.

CONFIGURATION FILES
snmpd checks for the existence of and parses the following files:

/etc/snmp/snmp.conf
Common configuration for the agent and applications. See snmp.conf(5) for details.

/etc/snmp/snmpd.conf

/etc/snmp/snmpd.local.conf
Agent-specific configuration. See snmpd.conf(5) for details. These files are optional and may be used to config-
ure access control, trap generation, subagent protocols and much else besides.

In addition to these two configuration files in /etc/snmp, the agent will read any files with the names snmpd.conf
and snmpd.local.conf in a colon separated path specified in the SNMPCONFPATH environment variable.

/usr/share/snmp/mibs/
The agent will also load all files in this directory as MIBs. It will not, however, load any file that begins with
a '.' or descend into subdirectories.