update
update is used to resynchronize the package index files from their sources. The indexes of available
packages are fetched from the location(s) specified in /etc/apt/sources.list. For example, when using
a Debian archive, this command retrieves and scans the Packages.gz files, so that information about
new and updated packages is available. An update should always be performed before an upgrade or
dist-upgrade. Please be aware that the overall progress meter will be incorrect as the size of the
package files cannot be known in advance.
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AND and OR lists are sequences of one of more pipelines separated by the && and || control operators,
respectively. AND and OR lists are executed with left associativity. An AND list has the form
command1 && command2
command2 is executed if, and only if, command1 returns an exit status of zero.
An OR list has the form
command1 || command2
command2 is executed if and only if command1 returns a non-zero exit status. The return status of AND
and OR lists is the exit status of the last command executed in the list.
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install
install is followed by one or more packages desired for installation or upgrading. Each package is a
package name, not a fully qualified filename (for instance, in a Debian GNU/Linux system, libc6 would
be the argument provided, not libc6_1.9.6-2.deb). All packages required by the package(s) specified
for installation will also be retrieved and installed. The /etc/apt/sources.list file is used to
locate the desired packages. If a hyphen is appended to the package name (with no intervening space),
the identified package will be removed if it is installed. Similarly a plus sign can be used to
designate a package to install. These latter features may be used to override decisions made by
apt-get's conflict resolution system.
A specific version of a package can be selected for installation by following the package name with
an equals and the version of the package to select. This will cause that version to be located and
selected for install. Alternatively a specific distribution can be selected by following the package
name with a slash and the version of the distribution or the Archive name (stable, testing,
unstable).
Both of the version selection mechanisms can downgrade packages and must be used with care.
This is also the target to use if you want to upgrade one or more already-installed packages without
upgrading every package you have on your system. Unlike the "upgrade" target, which installs the
newest version of all currently installed packages, "install" will install the newest version of only
the package(s) specified. Simply provide the name of the package(s) you wish to upgrade, and if a
newer version is available, it (and its dependencies, as described above) will be downloaded and
installed.
Finally, the apt_preferences(5) mechanism allows you to create an alternative installation policy for
individual packages.
If no package matches the given expression and the expression contains one of '.', '?' or '*' then it
is assumed to be a POSIX regular expression, and it is applied to all package names in the database.
Any matches are then installed (or removed). Note that matching is done by substring so 'lo.*'
matches 'how-lo' and 'lowest'. If this is undesired, anchor the regular expression with a '^' or '$'
character, or create a more specific regular expression.
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-y, --yes, --assume-yes
Automatic yes to prompts; assume "yes" as answer to all prompts and run non-interactively. If an
undesirable situation, such as changing a held package, trying to install a unauthenticated package
or removing an essential package occurs then apt-get will abort. Configuration Item:
APT::Get::Assume-Yes.
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