My potential hosting provider suggests to run a command in the terminal in order to make KVM based server's OS image minimal. Since their KVM templates come with packages I will not need, I thought I might use that same command to remove unwanted packages.
That command starts with DEBIAN_FRONTEND=noninteractive, then invoke apt-get remove as follows:
DEBIAN_FRONTEND=noninteractive apt-get remove --purge -y -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" package-1 package-2 ... package-n; apt-get -y autoremove; apt-get clean all It is the first time I encounter the DEBIAN_FRONTEND environment variable, and I could not find useful information so far. So I wonder what setting it to noninteractive does, and if it is advisable, because I suppose that value (noninteractive) would persist.
1 Answer
Simply prepending an apt command with DEBIAN_FRONTEND=something does not persist after the single command to which it is applied.
The DEBIAN_FRONTEND options are documented in the Section 7 manual pages of debconf (you may need to install the debconf-doc package in order to make these available on your system). From man 7 debconf:
Frontends One of debconf's unique features is that the interface it presents to you is only one of many, that can be swapped in at will. There are many debconf frontends available: dialog The default frontend, this uses the whiptail(1) or dialog(1) programs to display questions to you. It works in text mode. readline The most traditional frontend, this looks quite similar to how Debian configuration always has been: a series of questions, printed out at the console using plain text, and prompts done using the readline library. It even supports tab completion. The libterm-readline-gnu-perl package is strongly recommended if you chose to use this frontend; the default readline module does not support prompting with default values. At the minimum, you'll need the perl-modules package installed to use this frontend. This frontend has some special hotkeys. Pageup (or ctrl-u) will go back to the previous question (if that is supported by the package that is using debconf), and pagedown (or ctrl-v) will skip forward to the next question. This is the best frontend for remote admin work over a slow con‐ nection, or for those who are comfortable with unix. noninteractive This is the anti-frontend. It never interacts with you at all, and makes the default answers be used for all questions. It might mail error messages to root, but that's it; otherwise it is completely silent and unobtrusive, a perfect frontend for automatic installs. If you are using this front-end, and require non-default answers to questions, you will need to preseed the debconf database; see the section below on Unattended Package Installation for more details.It also notes that:
You can change the default frontend debconf uses by reconfiguring deb‐ conf. On the other hand, if you just want to change the frontend for a minute, you can set the DEBIAN_FRONTEND environment variable to the name of the frontend to use. For example: DEBIAN_FRONTEND=readline apt-get install slrn The dpkg-reconfigure(8) and dpkg-preconfigure(8) commands also let you pass --frontend= to them, followed by the frontend you want them to use. Note that not all frontends will work in all circumstances. If a fron‐ tend fails to start up for some reason, debconf will print out a mes‐ sage explaining why, and fall back to the next-most similar frontend.
