Bug 168947 - resolv.conf populated with empty search string
resolv.conf populated with empty search string
Product: Fedora
Classification: Fedora
Component: dhcp (Show other bugs)
i686 Linux
medium Severity medium
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Assigned To: Jason Vas Dias
Depends On:
  Show dependency treegraph
Reported: 2005-09-21 12:04 EDT by Scott R. Godin
Modified: 2007-11-30 17:11 EST (History)
0 users

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2005-09-22 16:12:02 EDT
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Regression: ---
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RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
log from dhclient (1.28 KB, text/plain)
2005-09-21 12:51 EDT, Scott R. Godin
no flags Details
resolv.conf file after running above commands (61 bytes, text/plain)
2005-09-21 12:53 EDT, Scott R. Godin
no flags Details
leases file (881 bytes, text/plain)
2005-09-21 12:55 EDT, Scott R. Godin
no flags Details

  None (edit)
Description Scott R. Godin 2005-09-21 12:04:32 EDT
From Bugzilla Helper:
User-Agent: Opera/8.5 (X11; Linux i686; U; en)

Description of problem:
Using a Netgear WGR614 v5 wireless router connected directly to the comcast 
cablemodem, I have my FC4 box set to get the information via DHCP for it's 
network info, and as well, the netgear box similarly. 

I checked the dhclient-script in its make_resolv_conf() subroutine, and it's 
*clean*.. i.e. it does what it's supposed to WRT filling in the 'search' field 
in resolv.conf -- if the field is empty, it won't write the string 'search  ' 
with no value, into resolv.conf (which is invalid and causes `host` to fail. 

However, apparently sometime after dhclient-script runs, something *else* is 
adding the empty search string back into resolv.conf such that the line

'search '

(minus the quotes) gets written to resolv.conf, causing failure of `host` and 
several other related commands. I have no idea what's causing this, and I've 

Every time the client updates dhcp, I have to go manually edit resolv.conf to 
remove the erroneous blank search line. 

Version-Release number of selected component (if applicable):
dhcp-3.0.2-22.FC4, dhclient-3.0.2-22.FC4

How reproducible:

Steps to Reproduce:
1. service network restart

Actual Results:  resolv.conf is populated with a 'search ' line that has no domain following it

Expected Results:  if the search domain is empty, whatever it is, shouldn't be writing "search " 
into resolv.conf, but it should either leave the line completely blank or not 
write anything at all.

Additional info:

I'll be happy to try and figure out which program/script is causing the problem 
if someone can just tell me how to log which apps are run in sequence, when 
started by a given process (such as service network restart)
Comment 1 Jason Vas Dias 2005-09-21 12:28:24 EDT
Do you use NetworkManager ? 
ie. does 'chkconfig --list NetworkManager' report 'on' for any runlevel ?
If so, it is responsible for writing resolv.conf, not dhclient.
No other app / script should be writing resolv.conf, AFAIK.
If so, can the problem be reproduced after you 'chkconfig --del NetworkManager'?
If not, please move this bug to 'NetworkManager'. If not, or if NetworkManager
was not enabled, read on.

Do you have an /etc/dhclient*.conf file ? If so, the search / nameserver
parameters could be overridden there - what are its contents ? 
Try removing it: 
 # mv /etc/dhclient*.conf /tmp

Please try this, for the ethX interface configured with DHCP:

# ifdown ethX
# cat /etc/resolv.conf
( should be empty, or have the initial contents you set up before dhclient
  was enabled. If it contains invalid parameters:
  # echo -n ''>/etc/resolv.conf
# rm -f /var/lib/dhcp/dhclient-ethX.leases
( ensure selinux is in "Permissive" mode, or you won't see any output from
  the next command:
  # setenforce 0
# dhclient -1 \
  -pf /var/run/dhclient-ethX.pid \
  -lf /var/lib/dhcp/dhclient-ethX.leases \
  2>&1 | tee /tmp/dhclient.log

when the dhclient command above completes:

1. Is the resolv.conf file correct or invalid ?

Please append these files to this bug report after the dhclient command above
has completed:
/tmp/dhclient.log   /etc/resolv.conf  /var/lib/dhcp/dhclient-eth0.leases

Then we should have enough information to resolve this bug report - thank you.
Comment 2 Scott R. Godin 2005-09-21 12:51:36 EDT
Created attachment 119084 [details]
log from dhclient
Comment 3 Scott R. Godin 2005-09-21 12:53:59 EDT
Created attachment 119085 [details]
resolv.conf file after running above commands
Comment 4 Scott R. Godin 2005-09-21 12:55:40 EDT
Created attachment 119086 [details]
leases file
Comment 5 Scott R. Godin 2005-09-21 12:58:14 EDT
all well and good except for the following: 
immediately after having done the above, I tried this: 

12:51pm {22} localhost:/root># service network restart
Shutting down interface eth0:                              [  OK  ]
Shutting down interface wlan0:                             [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:  
Determining IP information for eth0... done.
                                                           [  OK  ]
12:58pm {23} localhost:/root># cat /etc/resolv.conf
; generated by /sbin/dhclient-script

and look, there's the bug. ^^ 'search ' all by itself. Like I said, I'm at a 
loss to explain how it gets there. 
Comment 6 Scott R. Godin 2005-09-21 13:06:14 EDT
blah, forgot to attach the results of the commands you gave me before pasting 
the above. Here: 

12:43pm {2} localhost:/root># chkconfig --list NetworkManager
error reading information on service NetworkManager: No such file or directory

12:43pm {3} localhost:/root># ls /etc/dhclient*
ls: No match.

12:49pm {15} localhost:/root># ifdown eth0
12:49pm {16} localhost:/root># cat /etc/resolv.conf
; generated by /sbin/dhclient-script
12:49pm {17} localhost:/root># rm -f /var/lib/dhcp/dhclient-eth0.leases 
12:49pm {18} localhost:/root># setenforce 0
setenforce: SELinux is disabled
12:50pm {19} localhost:/root># dhclient -1 \
?   -pf /var/run/dhclient-ethX.pid \
?   -lf /var/lib/dhcp/dhclient-ethX.leases \
?   2>&1 | tee /tmp/dhclient.log
Ambiguous output redirect.
12:50pm {20} localhost:/root># bash
Wed Sep 21 12:50:39 EDT 2005
[root@localhost ~]# dhclient -1 \
>   -pf /var/run/dhclient-ethX.pid \
>   -lf /var/lib/dhcp/dhclient-ethX.leases \
>   2>&1 | tee /tmp/dhclient.log
Internet Systems Consortium DHCP Client V3.0.2-RedHat
Copyright 2004 Internet Systems Consortium.
All rights reserved.
For info, please visit http://www.isc.org/products/DHCP

/sbin/dhclient-script: configuration for eth1 not found. Continuing with 
/etc/sysconfig/network-scripts/network-functions: line 51: eth1: No such file or 
Listening on LPF/eth1/00:e0:18:a7:73:5e
Sending on   LPF/eth1/00:e0:18:a7:73:5e
Listening on LPF/eth0/00:20:18:d9:48:1e
Sending on   LPF/eth0/00:20:18:d9:48:1e
Listening on LPF/wlan0/00:12:17:71:a8:86
Sending on   LPF/wlan0/00:12:17:71:a8:86
Sending on   Socket/fallback
DHCPDISCOVER on eth1 to port 67 interval 5
DHCPDISCOVER on eth0 to port 67 interval 6
DHCPDISCOVER on wlan0 to port 67 interval 5
ip length 314 disagrees with bytes received 534.
accepting packet with data after udp payload.
DHCPREQUEST on eth0 to port 67
ip length 314 disagrees with bytes received 534.
accepting packet with data after udp payload.
DHCPREQUEST on wlan0 to port 67
ip length 314 disagrees with bytes received 534.
accepting packet with data after udp payload.
bound to -- renewal in 32577 seconds.
[root@localhost ~]# exit
12:50pm {21} localhost:/root># cat /etc/resolv.conf
; generated by /sbin/dhclient-script

as you can see, this works as expected, however see above.
Comment 7 Jason Vas Dias 2005-09-21 13:47:26 EDT
Your DHCP servers, on both eth1 and wlan0, are NOT supplying the 
'domain-name' option, so dhclient will not write it.
Neither do your dhcp servers set the dhcp host-name option.

I think I may have found the problem : is your hostname not set ?

Or - does the problem disappear when you put "HOSTNAME=myhostname"
in /etc/sysconfig/network-scripts ? (where "myhostname" is the name
you want to give your host).

The problem is in /etc/sysconfig/network-scripts/ifup-post, which does:

# don't set hostname on ppp/slip connections
if [ "$2" = "boot" -a \
     "${DEVICE}" != lo -a \
     "${DEVICETYPE}" != "ppp" -a \
     "${DEVICETYPE}" != "slip" ]; then
    if need_hostname; then
	IPADDR=`LANG= LC_ALL= ifconfig ${DEVICE} | grep 'inet addr' | 
		awk -F: '{ print $2 } ' | awk '{ print $1 }'`
	eval `/bin/ipcalc --silent --hostname ${IPADDR}`
	if [ "$?" = "0" ]; then
	    set_hostname $HOSTNAME

ie., if, after all the network scripts have been parsed for 'HOSTNAME=' or
'DNS=' or 'DOMAIN=' settings, and DHCP has brought up the interface (possibly
setting the hostname and search path), the hostname is still unset, the
ifup-post script will do a DNS lookup and unconditionally set the hostname .

After you've done a service network restart, what is your hostname set to ?

What is the output of the command:

# ipcalc --silent --hostname $IP

where $IP is the address of the interface that was brought up with DHCP (eth0)?

The problem is in /etc/sysconfig/network-scripts/network-functions, which
unconditionally sets the search path in resolv.conf to a possibly empty
search list:

set_hostname ()
    hostname $1
    if ! grep search /etc/resolv.conf >/dev/null 2>&1; then
	domain=`echo $1 | sed 's/^[^\.]*\.//'`
	rsctmp=`mktemp /tmp/XXXXXX`;
	cat /etc/resolv.conf > $rsctmp
	echo "search $domain" >> $rsctmp
	change_resolv_conf $rsctmp
	/bin/rm -f $rsctmp

The problem here is that the argument to this function may be empty, or may
not contain any '.'s . If it does not contain any '.'s, then the invalid line
   'search '
is added to resolv.conf, if the dhclient did not receive any 'domain-name'
option and resolv.conf contains no existing 'search' path - I'll raise a 
bug to get this fixed in initscripts.

If adding the HOSTNAME=myhostname to /etc/sysconfig/network does not resolve
your problem, please read on.

I made a mistake with the dhclient command above - you should have
appended the interface name - ie ran 'dhclient ... eth0' - sorry.
dhclient' ran for for eth1  which has no 
/etc/sysconfig/network-scripts/ifcfg-eth1 file, so the
'service network restart' command only brings up interface

Please could you retry for eth0:
# service network stop
# ifup lo
# rm -f /var/lib/dhclient-eth0.leases
# echo -n '' > /etc/resolv.conf
# dhclient -1 \
  -pf /var/run/dhclient-ethX.pid \
  -lf /var/lib/dhcp/dhclient-ethX.leases \
  eth0 \
  2>&1 | tee /tmp/dhclient.log

And then please append the contents of the /etc/resolv.conf, the
/var/lib/dhcp/dhclient-eth0.leases file, and the output of 'hostname' and 
'domainname' to this bug report - thank you.
Comment 8 Jason Vas Dias 2005-09-21 15:41:57 EDT
This text above:
> does the problem disappear when you put "HOSTNAME=myhostname"
> in /etc/sysconfig/network-scripts
should read:
> does the problem disappear when you put "HOSTNAME=myhostname"
> in /etc/sysconfig/network

IE. if you set the HOSTNAME= in /etc/sysconfig/network, the problem should
disappear, and no 'search' option will be written to resolv.conf, since
none was specified by the dhcp server.

If possible, get your dhcp server to send the domain-name option (and possibly
the host-name option).

If you cannot control what your dhcp server sends, then add this line to
default domain-name "my search path";
- then dhclient would write
search my search path
to /etc/resolv.conf.

If neither of the above solutions are sufficient, then please follow 
instructions above for gathering the 'dhclient eth0' session info.


Comment 9 Jason Vas Dias 2005-09-22 16:12:02 EDT
This problem can be resolved by:
  o Getting your dhcp server to supply the 'host-name' and / or 'domain-name'
  o Putting the
    option in /etc/sysconfig/network
  o Adding a mapping between the IP address you get on eth0 and your chosen 
    hostname to /etc/hosts:
'  myhostname.my.domain  myhostname

As such, it is not due to any bug in dhcp, but due to misconfiguration .

The bug about /etc/sysconfig/network-scripts/network-functions creating an
empty 'search ' path when no host name is configured and no host-name or
domain-name are sent by DHCP will be fixed in a future release of initscripts -
but the root cause is not configuring any host name or domain name for the host.

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