Why is my debian postinst script not being run?

Question

I have made a .deb of my app using fpm:

fpm -s dir -t deb -n myapp -v 9 -a all -x "*.git" -x "*.bak" -x "*.orig" \
--after-remove debian/postrm  --after-install debian/postinst \
--description "Automated build." -d mysql-client -d python-virtualenv home

Among other things, the postinst script is supposed to create a user for the app:

#!/bin/sh

    set -e

    APP_NAME=myapp

    case "$1" in
        configure)
            virtualenv /home/$APP_NAME/local
            #supervisorctl start $APP_NAME
        ;;

    # http://www.debian.org/doc/manuals/securing-debian-howto/ch9.en.html#s-bpp-lower-privs
       install|upgrade)

       # If the package has default file it could be sourced, so that
       # the local admin can overwrite the defaults

       [ -f "/etc/default/$APP_NAME" ] && . /etc/default/$APP_NAME

       # Sane defaults:

       [ -z "$SERVER_HOME" ] && SERVER_HOME=/home/$APP_NAME
       [ -z "$SERVER_USER" ] && SERVER_USER=$APP_NAME
       [ -z "$SERVER_NAME" ] && SERVER_NAME=""
       [ -z "$SERVER_GROUP" ] && SERVER_GROUP=$APP_NAME

       # Groups that the user will be added to, if undefined, then none.
       ADDGROUP=""

       # create user to avoid running server as root
       # 1. create group if not existing
       if ! getent group | grep -q "^$SERVER_GROUP:" ; then
          echo -n "Adding group $SERVER_GROUP.."
          addgroup --quiet --system $SERVER_GROUP 2>/dev/null ||true
          echo "..done"
       fi
       # 2. create homedir if not existing
       test -d $SERVER_HOME || mkdir $SERVER_HOME
       # 3. create user if not existing
       if ! getent passwd | grep -q "^$SERVER_USER:"; then
         echo -n "Adding system user $SERVER_USER.."
         adduser --quiet \
                 --system \
                 --ingroup $SERVER_GROUP \
                 --no-create-home \
                 --disabled-password \
                 $SERVER_USER 2>/dev/null || true
         echo "..done"
       fi

       # … and a bunch of other stuff.

It seems like the postinst script is being called with configure, but not with install, and I am trying to understand why. In /var/log/dpkg.log, I see the lines I would expect:

2012-06-30 13:28:36 configure myapp 9 9
2012-06-30 13:28:36 status unpacked myapp 9
2012-06-30 13:28:36 status half-configured myapp 9
2012-06-30 13:28:43 status installed myapp 9

I checked that /etc/default/myapp does not exist. The file /var/lib/dpkg/info/myapp.postinst exists, and if I run it manually with install as the first parameter, it works as expected.

Why is the postinst script not being run with install? What can I do to debug this further?

Answer 1

I think the example script you copied is simply wrong. postinst is not supposed to be called with any install or upgrade argument, ever. The authoritative definition of the dpkg format is the Debian Policy Manual. The current version describes postinst in chapter 6 and only lists configure, abort-upgrade, abort-remove, abort-remove, and abort-deconfigure as possible first arguments.

I don't have complete confidence in my answer, because your bad example is still up on debian.org and it's hard to believe such a bug could slip through.

Answer 2

I believe the answer provided by Alan Curry is incorrect, at least as of 2015 and beyond.
There must be some fault with the way the that your package is built or an error in the postinst file which is causing your problem.
You can debug your install by adding the -D (debug) option to your command line i.e.:

sudo dpkg -D2 -i yourpackage_name_1.0.0_all.deb

-D2 should sort out this type of issue

for the record the debug levels are as follows:

          Number   Description
               1   Generally helpful progress information
               2   Invocation and status of maintainer scripts
              10   Output for each file processed
             100   Lots of output for each file processed
              20   Output for each configuration file
             200   Lots of output for each configuration file
              40   Dependencies and conflicts
             400   Lots of dependencies/conflicts output
           10000   Trigger activation and processing
           20000   Lots of output regarding triggers
           40000   Silly amounts of output regarding triggers
            1000   Lots of drivel about e.g. the dpkg/info dir
            2000   Insane amounts of drivel

The install command calls the configure option and in my experience the postinst script will always be run. One thing that may trip you up is that the postrm script of the "old" version, if upgrading a package, will be run after your current packages preinst script, this can cause havoc if you don't realise what is going on.
From the dpkg man page: Installation consists of the following steps:

          1. Extract the control files of the new package.

          2.  If  another version of the same package was installed before
          the new installation, execute prerm script of the old package.

          3. Run preinst script, if provided by the package.

          4. Unpack the new files, and at the same time back  up  the  old
          files, so that if something goes wrong, they can be restored.

          5.  If  another version of the same package was installed before
          the new installation, execute the postrm script of the old pack‐
          age.  Note that this script is executed after the preinst script
          of the new package, because new files are written  at  the  same
          time old files are removed.

          6.  Configure the package. 

          Configuring consists of the following steps:

          1.  Unpack  the  conffiles, and at the same time back up the old
          conffiles, so that they can be restored if something goes wrong.

          2. Run postinst script, if provided by the package.