[Bug 1486654] [NEW] ssh-keygen fails to create keys when FQDN=64 chars

[Javier Bahillo]

Public bug reported:

According to RFC's a FQDN hostname may have up to 64 chars. Nevertheless
ssh-keygen fails to create a key when it has exactly these 64 chars:

Hostname (edited to hide , but with same amount of chars):

abcde-frontend-abcde-frontend-2-i-9b90b8d9.dyn.abcde.abcdfer.com

It fails with this message:
gethostname: File name too long

Not being able to create a key means that openssh-server postinst will
fail with this message:

Setting up openssh-server (1:6.6p1-2ubuntu1) ...
Creating SSH2 ED25519 key; this may take some time ...gethostname: File name too long
dpkg: error processing package openssh-server (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 openssh-server
E: Sub-process /usr/bin/dpkg returned an error code (1)


Tested on:
Ubuntu 14.04 LTS

openssh-client versions tested:
  Installed: 1:6.6p1-2ubuntu1
  Candidate: 1:6.6p1-2ubuntu2.3


Looks like s imilar bug report on RedHat bug tracker: https://bugzilla.redhat.com/show_bug.cgi?id=1097665

** Affects: openssh (Ubuntu)
     Importance: Undecided
         Status: New

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Title:
  ssh-keygen fails to create keys when FQDN=64 chars

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