My system configuration script does an apt-get install -y postfix. Unfortunately the script is halted when the postfix installer displays a configuration screen. Is there a method to force postfix to use the defaults during installation so that an automated script can continue to the end?
Does the postfix installer maybe check for existing configuration in /etc/postfix, and if it exists, not bother the user with the configuration screen?
You can use pre-seeding for this, using the debconf-set-selections command to pre-answer the questions asked by debconf before installing the package.
For example:
debconf-set-selections <<< "postfix postfix/mailname string your.hostname.com"
debconf-set-selections <<< "postfix postfix/main_mailer_type string 'Internet Site'"
apt-get install --assume-yes postfix
If you want this globally:
dpkg-reconfigure debconf
Then configure it to be "noninteractive"
If you just want it for single install run:
DEBIAN_FRONTEND=noninteractive apt-get install PACKAGE
When executing from a shell that does not offer here-strings (<<<), pipe the answers:
echo "postfix postfix/mailname string my.hostname.example" | debconf-set-selections
echo "postfix postfix/main_mailer_type string 'Internet Site'" | debconf-set-selections
DEBIAN_FRONTEND=noninteractive apt-get postfix
Another way it can be done is by creating a file e.g. myconf:
postfix postfix/main_mailer_type select Internet Site
postfix postfix/mailname string your.hostname3.com
Then call debconf-set-selections and pass the file as argument:
debconf-set-selections myconf
You can also do like other answers by piping the strings into debconf-set-selections instead:
echo "postfix postfix/main_mailer_type select Internet Site" | debconf-set-selections
echo "postfix postfix/mailname string your.hostname3.com" | debconf-set-selections
A way you can use the piping method is if you want to pass them from one server to another as described in the manpage using the sister command debconf-get-selections which is available in debconf-utils:
debconf-get-selections | ssh anotherserver debconf-set-selections
The temporary file where debconf-set-selections stores them is:
/var/cache/debconf/config.dat
You can check inside and it should contain the settings you just set:
Name: postfix/mailname
Template: postfix/mailname
Value: your.hostname3.com
Owners: postfix
Flags: seen
Name: postfix/main_mailer_type
Template: postfix/main_mailer_type
Value: Internet Site
Owners: postfix
Flags: seen
Then just run the installer and there will be no prompts:
apt install postfix -y
Now if you uninstall postfix:
apt remove postfix --purge
You will notice that there are no more postfix settings at all in /var/cache/debconf/config.dat at all, so if you decide to re-install postfix, and don't run debconf-set-selections again before, you will get the usual prompts.
