modify_resolvconf(8)

NAME

modify_resolvconf - modify /etc/resolv.conf

SYNOPSIS

modify_resolvconf modify -s <service> -t <text>|- -p <pro_
cess> [ -i <pid> ] -f <filename of script>  [  -e  <exten_
sion>  ] [ -l <list of search domains> | -d <domainname> ]
[ -n <list of nameservers> ] [ -a <filename> ] [ -o <file_
name> ] [ --resolv ] [ --named ] [ --no_restart ] [ -v ] [
-q ]
modify_resolvconf restore -s <service> [ -e <extension>  ]
[  -n  show  ]  [  -o  <filename>  ] [ -k ] [ --resolv ] [
--named ] [ --no_restart ] [ -v ] [ -q ]
modify_resolvconf cleanup [ -n show P ] [ -o <filename>  ]
[  -k ] [ --resolv ] [ --named ] [ --no_restart ] [ -v ] [
-q ]
modify_resolvconf check [ --resolv ] [ --named ] [ -v ]  [
-q ]
modify_resolvconf -h, --help

DESCRIPTION

modify_resolvconf can be used by programs that have to change /etc/resolv.conf or /etc/named.conf dynamically (temporarily). It provides a means to do that in a consis
tent way accross the system. The idea is to

- make a backup

that can be restored later. Therefore, a fixed nam
ing scheme is used (see below). Every modification
creates a new backup. These will be restored cor
rectly even if it happens in another sequence. If a
service crashes, there is a way to clean up stale
modification and to restore the original configura
tion.

- add an informational header

to the new configuration file that informs the user
(or other programs) that is was changed temporar
ily, who changed the file, why it was done and how
to avoid it in the future. This header is automati
cally created by modify_resolvconf and is therefore standardized. It is just the presence of this
header what marks it as temporarily modified.

- trigger needed actions

like restarting named if /etc/named.conf was changed or copy a modified /etc/resolv.conf to postfix's chroot environment.

It is recommended to make use of modify_resolvconf in every script that modifies /etc/resolv.conf or /etc/named.conf temporarily. It should not be used to write a definitive version of these files (e.g. by YaST or
some installation tool).

The naming scheme used for backup copies is:

/etc/resolv.conf.saved.by.<service name>.<extension>

where service name is one of e.g. dhclient, dhcpcd, pppd, ipppd, pcmcia, hotplug (these are the major candidates)
and private extension might optionally be used by the ser vice itself if it modifies twice, e.g. for different
interfaces.

This naming scheme allows restoring /etc/resolv.conf at boottime after a crash of the system or at starttime of
the service (after a crash of the service).

modify_resolvconf can be controlled with two variables in SuSE's /etc/sysconfig/network/config. With MOD IFY_RESOLV_CONF_DYNAMICALLY you can allow/disallow dynamic changes to /etc/resolv.conf. If you like /etc/named.conf to be modified instead, then set MODIFY_NAMED_CONF_DYNAMI CALLY to yes. Since it makes not much sense to write the
same nameservers to both files MODIFY_NAMED_CONF_DYNAMI CALLY has a higher priority then MODIFY_RESOLV_CONF_DYNAM ICALLY.

Programs which use modify_resolvconf don't need to respect these variables. They should call modify_resolvconf just always.

ACTIONS

modify write a new /etc/resolv.conf or /etc/named.conf

with the supplied data and create a backup of the
old one.

restore

take a backup of the given service (if it exists)
and restore it to the modified file. This might be
/etc/resolv.conf or /etc/named.conf itself or another backup which was made in between by any
other service. E.g. pcmcia modified
/etc/resolv.conf for an ethernet interface and after that ppp modifies it again for a modem con
nection. If you then eject the pcmcia card but keep
the modem connection, the backup made by pcmcia
will be restored to the backup made by ppp and
leave the /etc/resolv.conf or /etc/named.conf modi fied by ppp untouched.
If no extension was given it will remove all other
backups of the given service
(resolv.conf.saved.by.<service>*).

cleanup

remove all backups of /etc/resolv.conf and /etc/named.conf while trying to restore the origi nal ones. It does so for both /etc/resolv.conf and /etc/named.conf independently of the settings of the variables in /etc/sysconfig/network/config. If you want to clean up only for one of these then use
the --resolv or --named option.

check return 0 if /etc/resolv.conf has not been modified

dynamically and write a status message to stderr.
If /etc/resolv.conf has been modified dynamically, it returns 1 and echoes the text contained in the
Info: tag to stderr. br. Note that it always
checks /etc/resolv.conf independently of the set tings of the variables in /etc/sysconfig/net_ work/config. If you want to check /etc/named.conf then use --named because in certain situations you are interested in the state of exactly one of these
configuration files. E.g. if YaST wants to set new
definitive values to /etc/resolv.conf, it has to check if /etc/resolv.conf is modified currently and is not interested if /etc/named.conf was changed even if MODIFY_NAMED_CONF_DYNAMICALLY was set.

OPTIONS

-s, --service <service>

name of the service that requests the modification.
This will used for the name of the backup, and it
is put into the Modified_by tag of the info header
(see example below).

-e, --extension <string>

appends an additional extension to the backup file
name (this can be used by a service to create more
than one backup like for different ppp devices)

-p, --process <process>

name of the daemon that causes the modification (if
applicable)

-i, --pid <pid>

process ID of the daemon that causes the modifica
tion (if applicable)

-f, --script <filename>

some script is used by the daemon to request the
modification

-t, --text <text>

a text written to the informational header that
explains why the change was done and how to prevent
it in the future. If - is given as <text>, the text is read from stdin.

-l, --searchlist <list of search domains>

specifies a list of domains, separated by spaces
and protected by quotes, to be written to
/etc/resolv.conf as searchlist

-d, --domain <domainname>

the domain to be used

-n, --nameservers <list of nameservers>

the (space separated and quoted if necessary) list
of nameservers to be used

-o, --save_now <filename>

saves the current /etc/resolv.conf (/etc/named.conf) to the specified file. This may be used if you are interested in the modification
after restore or cleanup. Alternatively you can use
--save_later when modifying.

-a, --save_later <filename>

inserts an additional tag into the informational
header specifying a filename to use for an backup
of the modified configuration file to be done at
restore time. Alternatively you can use --save_now when restoring or cleaning up.

-k, --keep

if used with restore or cleanup it keeps the cur
rent (modified) resolver settings.

--resolv

restores, cleans up or checks /etc/resolv.conf independently of the settings of the variables in
/etc/sysconfig/network/config. This variable is ignored with 'modify'.

--named

restores, cleans up or checks /etc/named.conf inde pendently of the settings of the variables in
/etc/sysconfig/network/config. This variable is ignored with 'modify'.

--no_restart

does not trigger any actions like restarting named
or copying /etc/resolv.conf to the chroot environ ment of postfix.

-v, --verbose

be verbose

-q, --quiet

be quiet

-h, --help

show synopsis

EXAMPLE

This is an example for the /etc/resolv.conf that mod ify_resolvconf would create:

### BEGIN INFO
#
# Modified_by: dhcpcd
# Backup: /etc/resolv.conf.saved.by.dhclient
# Process: /sbin/dhcpcd
# Process_id: 12345
# Script:
#
# Info: blabla
# ...
#
### END INFO
search suse.de
nameserver 10.10.0.1
nameserver 10.10.0.2

FILES

/etc/resolv.conf
/etc/named.conf

BUGS

save_later does not work properly if restoring one
/etc/resolv.conf out of a stack of backups. Currently modify_resolvconf is dog slow, but this will be
enhanced in further versions.

SEE ALSO

resolv.conf(5), named.conf(5)

AUTHOR

Christian Zoz <zoz@suse.de>
Manual page by Peter Poeml <poeml@suse.de> and Christian

Zoz <zoz@suse.de>.