Comment 3 for bug 1328639

Here's what I get in a chroot

(utopic-amd64)root@utopic:/build# apt-get install gcc-doc
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
  gcc-4.9-doc
The following NEW packages will be installed:
  gcc-4.9-doc gcc-doc
0 upgraded, 2 newly installed, 0 to remove and 15 not upgraded.
Need to get 2169 kB of archives.
After this operation, 9220 kB of additional disk space will be used.
Do you want to continue? [Y/n]
Get:1 http://sherwood/ubuntu/ utopic-proposed/main gcc-4.9-doc all 4.9.0-6ubuntu1 [2165 kB]
Get:2 http://sherwood/ubuntu/ utopic/main gcc-doc amd64 4:4.9.0-3ubuntu1 [3702 B]
Fetched 2169 kB in 0s (4616 kB/s)
E: Can not write log (Is /dev/pts mounted?) - openpty (2: No such file or directory)
Selecting previously unselected package gcc-4.9-doc.
(Reading database ... 12003 files and directories currently installed.)
Preparing to unpack .../gcc-4.9-doc_4.9.0-6ubuntu1_all.deb ...
Unpacking gcc-4.9-doc (4.9.0-6ubuntu1) ...
Selecting previously unselected package gcc-doc.
Preparing to unpack .../gcc-doc_4%3a4.9.0-3ubuntu1_amd64.deb ...
Unpacking gcc-doc (4:4.9.0-3ubuntu1) ...
Setting up gcc-4.9-doc (4.9.0-6ubuntu1) ...
Setting up gcc-doc (4:4.9.0-3ubuntu1) ...
/var/lib/dpkg/info/gcc-doc.postinst: 3: /var/lib/dpkg/info/gcc-doc.postinst: install-info: not found
dpkg: error processing package gcc-doc (--configure):
 subprocess installed post-installation script returned error exit status 127
Errors were encountered while processing:
 gcc-doc
E: Sub-process /usr/bin/dpkg returned an error code (1)

and then if I install install-info

(utopic-amd64)root@utopic:/build# apt-get install install-info
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  install-info
0 upgraded, 1 newly installed, 0 to remove and 15 not upgraded.
1 not fully installed or removed.
Need to get 49.3 kB of archives.
After this operation, 267 kB of additional disk space will be used.
Get:1 http://sherwood/ubuntu/ utopic/main install-info amd64 5.2.0.dfsg.1-4 [49.3 kB]
Fetched 49.3 kB in 0s (701 kB/s)
E: Can not write log (Is /dev/pts mounted?) - openpty (2: No such file or directory)
Selecting previously unselected package install-info.
(Reading database ... 12028 files and directories currently installed.)
Preparing to unpack .../install-info_5.2.0.dfsg.1-4_amd64.deb ...
Unpacking install-info (5.2.0.dfsg.1-4) ...
Setting up install-info (5.2.0.dfsg.1-4) ...
Setting up gcc-doc (4:4.9.0-3ubuntu1) ...
install-info: No dir file specified; try --help for more information.
dpkg: error processing package gcc-doc (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 gcc-doc
E: Sub-process /usr/bin/dpkg returned an error code (1)

AFAICS both of these problems would be solved by using the trigger, or otherwise (if that doesn't work with the symlinks) then you need to modify the postinsts and prerms to pass /usr/share/info/dir to install-info.