.TH IFCHD 8 2012-07-20 Linux "Linux Administrator's Manual"
.SH NAME
ifchd \- interface change daemon
.SH SYNOPSIS
.B ifchd
.RI [ OPTION ]...
.SH DESCRIPTION
The ifchd daemon changes network interface configuration information
(such as the IP address, broadcast address, subnet, etc) as well as
resolv.conf, the machine hostname, and other similar system configuration
bits on the request of authorized clients such as ndhc instances.
.SH OPTIONS
.TP
.BR \-d ,\  \-\-detach
Immediately fork into the background.  This is the default behavior.
.TP
.BR \-n ,\  \-\-nodetach
Do not fork into the background.  Useful for debugging or initial setup.
.TP
.BR \-q ,\  \-\-quiet
Don't print to standard out, standard error, or syslog.
.TP
.BI \-c\  CHROOTDIR ,\ \-\-chroot= CHROOTDIR
This option specifies the directory to which ifchd should confine itself via
chroot() after startup.  This directory should be shared with associated ndhc
daemons, and should have access to dev/urandom and dev/null.  For logging to
work, a dev/log socket or device should also exist.
.TP
.BI \-r\  RESOLVCONF ,\ \-\-resolve= RESOLVCONF
Specifies the path to the system resolv.conf.  This file will typically be in
/etc/resolv.conf.  If this option is specified, ndhc will update the contents
of this file to match the DNS servers specified by the remote DHCP server.  If
this option is not specified, ifchd will never change the system DNS resolution
configuration.
.TP
.BR \-o ,\  \-\-hostname
If specified, ifchd will update the system host name in response to any
hostname option field provided by a remote DHCP server on the request of
a ndhc client.  If this option is not specified, ifchd will never change
the system hostname.
.TP
.BI \-p\  PIDFILE ,\ \-\-pidfile= PIDFILE
Write the process id number of the ifchd instance into the specified file name.
The default is to not write the process id number into any file at all.
.TP
.BI \-u\  USER ,\ \-\-user= USER
This option specifies the user name or user id that ifchd will change to after
startup.  This user should be unique to the ifchd daemon.
.TP
.BI \-g\  GROUP ,\ \-\-group= GROUP
This option specifies the group name or group id that ifchd will change to
after startup.
.TP
.BI \-U\  CLIENTUSER ,\ \-\-cuser= CLIENTUSER
This option specifies the user name or user id that will be required of
processes that wish to make interface change requests of ifchd.  Any other
users will be denied a connection to the ifchange socket.
.TP
.BI \-G\  CLIENTGROUP ,\ \-\-cgroup= CLIENTGROUP
This option specifies the group name or group id that will be required of
processes that wish to make interface change requests of ifchd.  Any other
groups will be denied a connection to the ifchange socket.
.TP
.BI \-P\  CLIENTPID ,\ \-\-cpid= CLIENTPID
This option specifies the process id that will be required to make interface
change requests of ifchd.  Any process that has a process id that does not
equal this value will be denied a connection to the ifchange socket.
.TP
.BI \-i\  INTERFACE ,\ \-\-interface= INTERFACE
Specifies an interface by name (such as 'eth0') on which ifchd is allowed to
make configuration changes (such as IP address, subnet mask, etc).  Multiple
interfaces may be whitelisted by using this switch multiple times.
.TP
.BR \-V ,\  \-\-verbose
Print detailed messages.  Useful for debugging or setup.
.TP
.BR \-h ,\  \-\-help
Print basic help information and exit.
.TP
.BR \-v ,\  \-\-version
Display the ifchd version number and copyright information.
.SH SIGNALS
It is not necessary to sleep between sending signals, as signals received are
processed sequentially in the order they are received.  ifchd does not
perform any unusual behavior on receipt of signals.
.SH NOTES
ifchd is rather minimal and doesn't do exotic things like change NTP server
configuration.  This is intentional, since it needs to run as CAP_NET_ADMIN,
which although far less powerful than root, still gives it a fair amount
of privileged behavior.