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Following is the first few entries in /var/log/apt/history.log from a fresh installation of Debian 7.0:

Start-Date: 2013-05-09  20:02:18
Commandline: apt-get -o APT::Status-Fd=4 -o APT::Keep-Fds::=5 -o APT::Keep-Fds::=6 -q -y --no-remove install locales
Install: locales:amd64 (2.13-38)
End-Date: 2013-05-09  20:02:19

Start-Date: 2013-05-09  22:03:06
Commandline: apt-get -o APT::Status-Fd=4 -o APT::Keep-Fds::=5 -o APT::Keep-Fds::=6 -q -y --no-remove install busybox
Install: busybox:amd64 (1.20.0-7)
End-Date: 2013-05-09  22:03:07

Start-Date: 2013-05-09  22:03:07
Commandline: apt-get -o APT::Status-Fd=4 -o APT::Keep-Fds::=5 -o APT::Keep-Fds::=6 -q -y --no-remove install initramfs-tools
Install: libklibc:amd64 (2.0.1-3.1, automatic), klibc-utils:amd64 (2.0.1-3.1, automatic), initramfs-tools:amd64 (0.109.1)
End-Date: 2013-05-09  22:03:08

What is the meaning of these options:

-o APT::Status-Fd=4 -o APT::Keep-Fds::=5 -o APT::Keep-Fds::=6

I cannot find them in the apt-get manpage.

share|improve this question
Those are Perl lines, they look like variables being set to those values. Do you want to know what they are used for? – slm Sep 10 '13 at 12:25
@slm It's not Perl, it's APT configuration syntax, and I think it's descended from C++ without going via Perl. – Gilles Sep 10 '13 at 21:36
up vote 3 down vote accepted

Those would be debconf-apt-progress descriptors. Used to display the progress bar when apt calls the debconf-apt-progress wrapper.
Output on File Descriptor 4, reserve File Descriptors 5 and 6.

man 1 debconf-apt-progress
debconf-apt-progress installs packages using debconf to display a progress bar.
The given command should be any command-line apt frontend; specifically, it must send progress information to the file descriptor selected by the APT::Status-Fd configuration option, and must keep the file descriptors nominated by the APT::Keep-Fds configuration option open when invoking debconf (directly or indirectly), as those file descriptors will be used for the debconf passthrough protocol.

You can find more about them in the man -k apt instead of man apt-get.

share|improve this answer
man apt makes no mention of debconf-apt-progress; it's almost a dummy manpage. – Tshepang Sep 10 '13 at 12:44
oops, that should have been man -k apt. there is some cruft to wade through but most of it has to do with apt or aptitude - I will edit – Yuugian Sep 10 '13 at 15:13

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