![]() Sometimes the system does not have all the keys it needs and runs into this issue. The apt packaging system has a set of trusted keys that determine whether a package can be authenticated and therefore trusted to be installed on the system. For example: $ sudo apt-get upgradeĮ: Some packages could not be authenticated If these errors aren’t fixed, apt will have problems when installing or upgrading packages. W: GPG error: trusty-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32 W: GPG error: trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32 W: GPG error: trusty-security Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32 You can learn more by reading the apt-get and apt manual pages.There are times when running apt-get update in Ubuntu will result in error messages such as the following: $ sudo apt-get update It does not capture all possible uses of apt-get, plus there are a number of other utilities provided in the APT suite, such as apt-cache for examining information about installed and available packages. To deleted cached package installer files, but only for packages that are unlikely to be needed again (i.e., those that are so old they've been removed from the servers, as of last time sudo apt-get update was run): sudo apt-get autoclean deb) files (which does not remove any packages, but will make it so they have to be fetched over the network again to be reinstalled): sudo apt-get clean To reinstall a package and delete its systemwide configuration files while doing so: sudo apt-get -purge -reinstall install. To reinstall a package, run: sudo apt-get -reinstall install. ![]() To do that, and also remove their global configuration files" sudo apt-get -purge autoremove To remove packages that were installed automatically because other packages needed them, but which now are no longer needed, run: sudo apt-get autoremove To remove a package and also remove its systemwide configuration files (but not its per-user configuration files, which reside in users' home directories), run: sudo apt-get purge. To remove one or more packages (i.e., to uninstall it), run: sudo apt-get remove. with the list of packages you want to install (if you want to install more than one package, put spaces between the package names): sudo apt-get install. To install one or more packages, run this, replacing. To upgrade packages, including packages that require uninstalled packages to be installed, or installed packages to be removed, run this (but be careful-it's best to pay attention to what will be added or removed): sudo apt-get dist-upgrade To upgrade packages (i.e., "update your system"), run: sudo apt-get upgrade To update information about what packages are available and from where (which you should do before attempting to upgrade or install any packages with apt-get), run: sudo apt-get update That's what you should probably be using. The most commonly used APT command is apt-get. See Fsando's answer forĪPT is a suite of utilities, including a database of information about what packages are available from where.ĪPT is not a single command. Not support all the same actions and options as apt-get, it may often be used in place of apt-get. Various other apt- commands (e.g., apt-get, apt-cache), withĬolorized display and progress bars. TheĪpt command provides a convenient subset of the functionality of Starting in Ubuntu 14.04, there is a command in Ubuntu called justĪpt, which didn't exist when this question was originally asked.
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