It is good practice to verify the integrity of the distribution files.
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It is essential that you verify the integrity of the downloaded files using the PGP signature or the SHA1 or MD5 checksums. The checksums are not as strong indicators as the PGP signature.
The PGP signatures can be verified using PGP or GPG. First download the KEYS as well as the asc signature file for the particular distribution. Make sure you get these files from the main distribution directory, rather than from a mirror. Then verify the signatures using
% pgpk -a KEYS
% pgpv release_name.tar.gz.asc
% pgp -ka KEYS
% pgp release_name.tar.gz.asc
% gpg --import KEYS
% gpg --verify release_name.tar.gz.asc
Alternatively, you can verify the checksums on the files. Unix programs called md5/sha1 or md5sum/sha1sum are included in many unix distributions. *sum is also available as part of GNU Textutils. Windows users can get binary md5 programs from http://www.fourmilab.ch/md5 and hhttp://www.pc-tools.net/win32/freeware/console. Windows SlavaSoft fsum supports MD5 and SHA1.
We highly recommend verifying the PGP signature, though.