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Accepted
Ben Williams
Asked: 2011-08-03 22:46:31 +0800 CST

Bash prompt on Ubuntu - FQDN (\H) same as hostname (\h)

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We've got seperate environments at my workplace for development, testing, integration, and staging.

Within those envs, we've overloaded the hostnames in DNS - e.g. in the dev environment, the primary web machine is called web1.dev.example.com, and in the test environment, the primary web machine is web1.test.example.com.

To distinguish between machines in the different environments, I want to customise the bash prompts to display the FQDN rather than just the hostname. Well and good; I should be able to replace \h with \H in $PS1, right? Hmm. They show the exact same thing.

me@web1:~$ hostname
web1
me@web1:~$ hostname -f
web1.dev.example.com
me@web1:~$ export PS1="\[\u@\h: \w\]\$ "
me@web1: ~$ export PS1="\[\u@\H: \w\]\$ "
me@web1: ~$

In /etc/hostname, I've got just the hostname (web1). hostname and hostname -f both return the correct results ("web1" and "web1.test.example.com" respectively), and I've got the correct entries in /etc/hosts.

What gives?

These are Ubuntu 10.04 hosts, if that makes a difference.

ubuntu bash fqdn

3 Answers

  1. Best Answer

    Try using an explicit call to hostname -f to get the fqdn of the system

    export PS1="\[\u@$(hostname -f): \w\]\$ "

    e.g. 

    iain$ export PS1="\[\u@$(hostname -f): \w\]\$ "
[email protected]: ~$

    EDIT:

    Further research shows that the contents of /etc/hostname (Ubuntu) and /etc/sysconfig/network (CentOS) are relevant. If the FQDN is in the file then the \H works correctly.

    The hostname(1) man page for Ubuntu does though say that you shouldn't put the FQDN in /etc/hostname but gives no reason as to why.

    • 24

  2. There is an insane amount of craziness about hostnames, short and long, and getting it right all the time is hard -- so I just give up and make everything use the FQDN as the hostname...

    I do the same thing as you in my environments, but I chop down the FQDNs in the prompt because I know what site I'm on, and it saves space. I also colour-code my prompt based on environment so I've got a better warning of when I'm doing something somewhere "important". I also space-separate the path from everything else, to make it easy to copy-pasta pwd. A snippet from my stock /etc/profile:

    if hostname -f | grep -q '\.stg\.example\.com'; then
  _ROOT_COLOR=33  # yellow
  _USER_COLOR=36  # cyan
else
  _ROOT_COLOR=31  # red
  _USER_COLOR=32  # green
fi

if [ "`id -u`" -eq 0 ]; then
  PS1="\[\033[01;${_ROOT_COLOR}m\]$(hostname -f|sed 's/\.example\.com//')\[\033[01;34m\] \w #\[\033[00m\] "
else
  PS1="\[\033[01;${_USER_COLOR}m\]\u@$(hostname -f|sed 's/\.example\.com//')\[\033[01;34m\] \w $\[\033[00m\] "
fi

    And, as far as "ugliness" goes, who cares what the code to display the prompt looks like? It's write-only code most of the time, anyway.

    • 5

  3. That is a bug with how Ubuntu manages /etc/hostname.

    Bug filed: https://bugs.launchpad.net/ubuntu/+source/bash/+bug/1276796

    • 0