NETDUMP(4)             FreeBSD Kernel Interfaces Manual             NETDUMP(4)

NAME
     netdump - protocol for transmitting kernel dumps to a remote server

SYNOPSIS
     To compile netdump client support into the kernel, place the following
     line in your kernel configuration file:

           options NETDUMP

DESCRIPTION
     netdump is a UDP-based protocol for transmitting kernel dumps to a remote
     host.  A netdump client is a panicking kernel, and a netdump server is a
     host running the netdump daemon, available in ports as
     ports/ftp/netdumpd.  netdump clients are configured using the dumpon(8)
     utility or the netdump command in ddb(4).

     netdump client messages consist of a fixed-size header followed by a
     variable-sized payload.  The header contains the message type, a sequence
     number, the offset of the payload data in the kernel dump, and the length
     of the payload data (not including the header).  The message types are
     HERALD, FINISHED, KDH, VMCORE, and EKCD_KEY.  netdump server messages
     have a fixed size and contain only the sequence number of the client
     message.  These messages indicate that the server has successfully
     processed the client message with the corresponding sequence number.  All
     client messages are acknowledged this way.  Server messages are always
     sent to port 20024 of the client.

     To initiate a netdump, the client sends a HERALD message to the server at
     port 20023.  The client may include a relative path in its payload, in
     which case the netdump server should attempt to save the dump at that
     path relative to its configured dump directory.  The server will
     acknowledge the HERALD using a random source port, and the client must
     send all subsequent messages to that port.

     The KDH, VMCORE, and EKCD_KEY message payloads contain the kernel dump
     header, dump contents, and dump encryption key respectively.  The offset
     in the message header should be treated as a seek offset in the
     corresponding file.  There are no ordering requirements for these
     messages.

     A netdump is completed by sending the FINISHED message to the server.

     The following network drivers support netdump: alc(4), bge(4), bnxt(4),
     bxe(4), cxgb(4), em(4), igb(4), ix(4), ixl(4), mlx4en(4), mlx5en(4),
     re(4), vtnet(4).

SYSCTL VARIABLES
     The following variables are available as both sysctl(8) variables and
     loader(8) variables:

     net.netdump.debug
             Control debug message verbosity.  Debug messages are disabled by
             default, but are useful when troubleshooting or when developing
             driver support.

     net.netdump.path
             Specify a path relative to the server's dump directory in which
             to store the dump.  For example, if the netdump server is
             configured to store dumps in /var/crash, a path of "foo" will
             cause the server to attempt to store dumps from the client in
             /var/crash/foo.  The server will not automatically create the
             relative directory.

     net.netdump.polls
             The client will poll the configured network interface while
             waiting for acknowledgements.  This parameter controls the
             maximum number of poll attempts before giving up, which typically
             results in a re-transmit.  Each poll attempt takes 0.5ms.

     net.netdump.retries
             The number of times the client will re-transmit a packet before
             aborting a dump due to a lack of acknowledgement.  The default
             may be too small in environments with lots of packet loss.

     net.netdump.arp_retries
             The number of times the client will attempt to learn the MAC
             address of the configured gateway or server before giving up and
             aborting the dump.

SEE ALSO
     decryptcore(8), dumpon(8), savecore(8)

HISTORY
     netdump client support first appeared in FreeBSD 12.0.

BUGS
     Only IPv4 is supported.

     netdump may only be used after the kernel has panicked.

FreeBSD 13.1-RELEASE-p6         August 25, 2020        FreeBSD 13.1-RELEASE-p6