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If I use apt-get install -qq mono-devel, I expect it to be quiet except for errors, according to the help:

-qq No output except for errors

Instead I get:

Extracting templates from packages: 100%

Selecting previously unselected package binfmt-support.

(Reading database ... 84711 files and directories currently installed.)

Unpacking binfmt-support (from .../binfmt-support_2.0.8_i386.deb) ...

Selecting previously unselected package cli-common.

Unpacking cli-common (from .../cli-common_0.8.2_all.deb) ...

Selecting previously unselected package libgdiplus.

Unpacking libgdiplus (from .../libgdiplus_2.10-3_i386.deb) ...

Selecting previously unselected package libmono-2.0-1.

Unpacking libmono-2.0-1 (from .../libmono-2.0-1_2.10.8.1-1ubuntu2.2_i386.deb) ...

Selecting previously unselected package libmono-2.0-dev.

Unpacking libmono-2.0-dev (from .../libmono-2.0-dev_2.10.8.1-1ubuntu2.2_i386.deb) ...

Selecting previously unselected package libmono-corlib4.0-cil.

Unpacking libmono-corlib4.0-cil (from .../libmono-corlib4.0-cil_2.10.8.1-1ubuntu2.2_all.deb) ...

Selecting previously unselected package libmono-system-xml4.0-cil.

Unpacking libmono-system-xml4.0-cil (from .../libmono-system-xml4.

and more...

In fact, a couple hundred lines worth of output. This does not appear to match up with no output except for errors.

How do I actually get apt-get install to print out only when there are errors keeping it from installing?

The man page for apt-get is as follows:

NAME

       apt-get - APT package handling utility -- command-line interface



SYNOPSIS

       apt-get [-asqdyfmubV] [-o=config_string] [-c=config_file] [-t=target_release]

               [-a=architecture] {update | upgrade | dselect-upgrade | dist-upgrade |

               install pkg [{=pkg_version_number | /target_release}]...  | remove pkg...  |

               purge pkg...  | source pkg [{=pkg_version_number | /target_release}]...  |

               build-dep pkg [{=pkg_version_number | /target_release}]...  |

               download pkg [{=pkg_version_number | /target_release}]...  | check | clean |

               autoclean | autoremove | {-v | --version} | {-h | --help}}

The -q or -qq flag should go before the command, like so:

apt-get -qq upgrade

A simple redirection could do this. It's not exactly what you had in mind, I'm sure, but it sure as hell works :)

In short, just whack > /dev/null on the end of any command where you want to redirect all the stdout into nothingness. Things outputted on stderr will still show in the console.

$ sudo apt-get update > /dev/null

[sudo] password for oli: 

$ 

No junk! And here's what happens if we're silly and break something:

$ apt-get cheese > /dev/null

E: Invalid operation cheese

$

We faced the same problem. apt-get install -qq removes most of the outputs but annoying "(Reading database ..." still persist.

We took a look in the source of apt and discover that the output is produced by dpkg that was forked by apt. Then the source of dpkg shows that the annoying soutput is only issued when isatty(1) is true. This is only the case when the fork uses pty instead pipe. Back to apt, there is a undocumented configuration variable that allows to use pipe instead pty which then solve the problem:

apt-get install -qq -o=Dpkg::Use-Pty=0 <packages>

Expecting that can help others.

As you can see here and here

You can do:

export DEBIAN_FRONTEND=noninteractive

apt-get -yq install [packagename]

export DEBIAN_FRONTEND=dialog

Or one line:

DEBIAN_FRONTEND=noninteractive apt-get -yq install [packagename]