I'm trying to connect from a 10.04 system to a 12.04 system via SSH. Strangely enough the rules in resolv.conf seem to take effect only selectively, which leaves me puzzled. Observe:

[2] user@mach:~$ ssh pangolin

ssh: Could not resolve hostname pangolin: Name or service not known

[2] user@mach:~$ host pangolin

pangolin.subdomain.domain.tld has address 172.16.7.12

subdomain.domain.tld is on the search line in /etc/resolv.conf and using host the name is properly searched given those rules. However, with the SSH client ssh I receive the error reproduced above. How can this be? I was always of the impression that the name resolution rules in resolv.conf apply system-global.

Note: /etc/hosts doesn't declare the name pangolin at all. The package openssh-server is configured on the target machine. The question is purely about why name resolution isn't consistent between those two programs.

Another note: the command works fine when I enter the fully-qualified domain name, i.e. pangolin.subdomain.domain.tld.

Meanwhile I rebooted the client machine (10.04) and the problem still exists. A DNS caching daemon isn't installed, so I reckon that shouldn't have been a problem anyway.

The information asked for in the comment:

$ grep host /etc/nsswitch.conf

hosts:          files dns

/etc/resolv.conf, I transformed the domain names consistently:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)

#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

nameserver 172.16.1.1

nameserver 172.16.1.5

search subdomain.domain1.com domain1.com domain2 domain3.com domain2.ccTLD domain3.net dev.domain1.com sdk.dev.domain1.com

... and the full /etc/nsswitch.conf:

$ cat /etc/nsswitch.conf

# /etc/nsswitch.conf

#

# Example configuration of GNU Name Service Switch functionality.

# If you have the `glibc-doc-reference' and `info' packages installed, try:

# `info libc "Name Service Switch"' for information about this file.



passwd:         compat

group:          compat

shadow:         compat



hosts:          files dns

networks:       files



protocols:      db files

services:       db files

ethers:         db files

rpc:            db files



netgroup:       nis

... and /etc/network/interfaces, which is the source for resolv.conf in 12.04:

# This file describes the network interfaces available on your system

# and how to activate them. For more information, see interfaces(5).



# The loopback network interface

auto lo

iface lo inet loopback



# The primary network interface

auto eth0

iface eth0 inet static

        address 172.16.1.234

        netmask 255.255.0.0

        gateway 172.16.255.254

        dns-nameservers 172.16.1.1 172.16.1.5

        dns-search domain1.com. domain2. domain3.com. domain2.ccTLD. domain3.net. dev.domain1.com. sdk.dev.domain1.com. subdomain.domain1.com.

        dns-domain subdomain.domain1.com.

Note: the transformation of the domain names was done with sed, so it's consistent between the various reproduced files.

There is no ~/.ssh/config, but here's the global one (/etc/ssh/ssh_config), shrunk for the sake of brevity:

$ grep -v '^#' /etc/ssh/ssh_config |grep -v '^[[:space:]]*$'

Host *

    SendEnv LANG LC_*

    HashKnownHosts yes

    GSSAPIAuthentication yes

    GSSAPIDelegateCredentials no

$ mtr pangolin

Name or service not known: Success