Man Linux: Main Page and Category List


       ucarp — Automatic IP failover


       ucarp [-i, --interface=INTERFACE]  [-s, --srcip=IPADDRESS]
       [-v, --vhid=VHID]  [-p, --pass=PASSWORD]  [-o, --passfile=PASSFILE]
       [-P, --preempt]  [-n, --neutral]  [-a, --addr=IPADDR]  [-h, --help]
       [-b, --advbase=SECS]  [-k, --advskew=SKEW]  [-u, --upscript=SCRIPT]
       [-d, --downscript=SCRIPT]  [-r, --deadratio=RATIO]  [-z, --shutdown]
       [-B,  --daemonize]   [-f,  --facility=FACILITY]   [-x,  --xparam PARAM]
       [-S, --ignoreifstate]  [-M, --nomcast]


       ucarp allows a pair of hosts to share common IP addresses in  order  to
       provide  automatic  failover of an address from one machine to another.
       It is a portable userland implementation of the secure and  patent-free
       Common  Address  Redundancy  Protocol, (CARP), OpenBSD’s alternative to


       ucarp supports the following command line options:

       -i INTERFACE --interface=INTERFACE
                 The network interface to bind to.

       -s IPADDRESS --srcip=IPADDRESS
                 The persistent source address,  (real  IP),  associated  with
                 this interface.

       -v VHID --vhid=VHID
                 The id of the virtual server [1-255].

       -p PASSWORD --pass=PASSWORD
                 The  shared password, (this gets encrypted and is not sent in
                 the clear).

       -o PASSFILE --passfile=PASSFILE
                 File to read the shared password  from.  The  file  specified
                 should contain the password on the first line of the file.

       -P --preempt
                 Turn on preemptive failover. This causes an instance of ucarp
                 to assume master status right immediately.

       -n --neutral
                 Do not run the downscript on startup when the  initial  state
                 is backup.

       -a IPADDRESS --addr=IPADDRESS
                 The IP address of the virtual server.

       -h --help Display a brief summary of the command line options.

       -b SECONDS --advbase=SECONDS
                 Interval in seconds that advertisements will occur, (defaults
                 to 1 second).

       -k SKEW --advskew=SKEW
                 Advertisement skew [1-255], (defaults to 0).

       -u COMMAND --upscript=COMMAND
                 Specifies the command to run  after  ucarp  has  successfully
                 become master, the interface name gets passed as an argument.
                 Typically a script used to bring up the virtual address,  log
                 the result, add routes, clear arp cache entries, etc.

       -d COMMAND --downscript=COMMAND
                 Specifies   the   command   that   is  run  after  ucarp  has
                 transitioned to the  backup  state,  the  interface  name  is
                 passed  as  an  argument.  This is typically a script used to
                 bring down the virtual  interface,  log  the  action,  remove
                 routes, etc.

       -r RATIO --deadratio=RATIO
                 Ratio used by the backup to determine how long to wait for an
                 unresponsive master before considering it dead.

       -z --shutdown
                 Use of this command causes the command specified  by  the  -d
                 argument to be invoked when ucarp shuts down.

       -B --daemonize
                 Causes  ucarp  to  detach  from  the  terminal and run in the
                 background as a daemon.

       -f --facility
                 Set the syslog facility, defaults to daemon.

       -x PARAMETER --xparam=PARAMETER
                 Specify an extra parameter to  be  supplied  to  the  up/down

       -S --ignoreifstate
                 Ignore  unplugged  network cables. This option is useful when
                 ucarp nodes are connected with  a  crossover  cable.  Without
                 this  option  the  master  will transition to backup when the
                 other node is powered down, as it no longer has a  link  (NO-

       -M --nomcast
                 Use broadcast instead of multicast advertisements.


       A  host  with  a  real IP of configured to be the master in a
       preemptive configuration with a virtual IP of

           ucarp -i eth0 -s -v 10 -p secret -a \
           --upscript=/etc/ --downscript=/etc/ -P

       The backup might be configured something like this.

           ucarp -i eth0 -s -v 10 -p secret -a \
           --upscript=/etc/ --downscript=/etc/

       A machine with a real IP of is the preferred master for  a
       virtual IP of, broadcasts are sent every 5 seconds.

           ucarp -b 5 -s -v 27 -p badpass -a \
           -u /etc/ -d /etc/ -z

       The  hot standby with an IP of uses the following command,
       (note the advskew of 50 putting it at a  disadvantage  and  making  the
       first machine preferred).

           ucarp -b 5 -k 50 -s -v 27 -p badpass -a \
           -u /etc/ -d /etc/ -z


       ucarp was written by Frank Denis, <>.

       This  manual page was written by Eric Evans <> for the
       Debian system (but may be used by others).  Permission  is  granted  to
       copy, distribute and/or modify this document under the terms of the GNU
       General Public License, Version 2 or any later version published by the
       Free Software Foundation.

       On  Debian systems, the complete text of the GNU General Public License
       can be found in /usr/share/common-licenses/GPL.