Today I checked out my upgrades and saw 63 upgrades in Debian testing. Fine. I got curious because most of them are held back, so I used -V to see the versions. To my surprise, most of them where upgrading to +b1 or +b2 versions. Like a good boy I do apt-get changelog libc6 (yeah, that one is important) just to see that the changelog has no +b1 version. So, what are these versions for?sudo apt-get -V upgradeReading package lists... DoneBuilding dependency tree       Reading state information... DoneThe following packages have been kept back:   gdm3 (3.4.1-9 => 3.4.1-9+b1)   libalgorithm-diff-xs-perl (0.04-2+b2 => 0.04-2+b3)   libapt-pkg-perl (0.1.29 => 0.1.29+b1)   libcairo-perl (1.103-2 => 1.103-2+b1)   libclass-c3-xs-perl (0.13-1+b2 => 0.13-1+b3)   libclone-perl (0.34-1 => 0.34-1+b1)   libcrypt-blowfish-perl (2.14-1 => 2.14-1+b1)   libcrypt-openssl-bignum-perl (0.04-4 => 0.04-4+b1)   libcrypt-ssleay-perl (0.58-1 => 0.58-1+b1)   libdbd-mysql-perl (4.023-1 => 4.023-1+b1)   libdbi-perl (1.628-1 => 1.628-1+b1)   libdigest-crc-perl (0.18-1+b1 => 0.18-1+b2)   libdigest-md4-perl (1.9+dfsg-1 => 1.9+dfsg-1+b1)   libfile-fcntllock-perl (0.14-2 => 0.14-2+b1)   libfile-fnmatch-perl (0.02-1+b2 => 0.02-1+b3)   libglib-perl (1.301-1 => 1.301-1+b1)   libgtk2-perl (1.247-2 => 1.247-2+b1)   libhtml-parser-perl (3.71-1 => 3.71-1+b1)   libio-pty-perl (1.08-1+b2 => 1.08-1+b3)   libjson-xs-perl (2.340-1 => 2.340-1+b1)   liblist-moreutils-perl (0.33-1+b1 => 0.33-1+b2)   liblocale-gettext-perl (1.05-7+b1 => 1.05-7+b2)   libmath-bigint-gmp-perl (1.37-2 => 1.37-3)   libnet-dbus-perl (1.0.0-2 => 1.0.0-2+b1)   libnet-dns-perl (0.68-1.1 => 0.68-1.2)   libnet-pcap-perl (0.17-1 => 0.17-1+b1)   libnet-rawip-perl (0.25-1+b2 => 0.25-1+b3)   libnet-ssleay-perl (1.55-1 => 1.55-1+b2)   libpam-systemd (44-12 => 44-12+b1)   libpango-perl (1.224-2 => 1.224-2+b1)   libparams-util-perl (1.07-1 => 1.07-1+b1)   libpurple0 (2.10.7-2 => 2.10.7-2+b1)   libsocket-perl (2.011-1 => 2.011-1+b1)   libsocket6-perl (0.23-1+b2 => 0.23-1+b3)   libsub-name-perl (0.05-1+b2 => 0.05-1+b3)   libsvn1 (1.6.17dfsg-4.1+b1 => 1.7.9-1+nmu4)   libterm-readkey-perl (2.30-4+b2 => 2.30-4+b3)   libterm-readline-gnu-perl (1.20-2+b1 => 1.20-2+b2)   libtext-charwidth-perl (0.04-7+b1 => 0.04-7+b2)   libtext-iconv-perl (1.7-5 => 1.7-5+b1)   libuuid-perl (0.02-5 => 0.02-5+b1)   libxml-libxml-perl (2.0010+dfsg-1 => 2.0010+dfsg-1+b1)   libxml-parser-perl (2.41-1+b1 => 2.41-1+b2)   libyaml-libyaml-perl (0.38-3 => 0.38-3+b1)   perl (5.14.2-21 => 5.18.1-3)   perl-base (5.14.2-21 => 5.18.1-3)   perl-modules (5.14.2-21 => 5.18.1-3)   perl-tk (804.031-1 => 804.031-1+b1)   subversion (1.6.17dfsg-4.1+b1 => 1.7.9-1+nmu4)   systemd (44-12 => 44-12+b1)   vim (7.3.923-3 => 7.3.923-3+b1)   vim-common (7.3.923-3 => 7.3.923-3+b1)   vim-gtk (7.3.923-3 => 7.3.923-3+b1)   xchat (2.8.8-7.1 => 2.8.8-7.1+b1)   xserver-xorg-core (1.12.4-6.1 => 1.12.4-6.2+b1)The following packages will be upgraded:   libc-dev-bin (2.17-92 => 2.17-92+b1)   libc6 (2.17-92 => 2.17-92+b1)   libc6-dbg (2.17-92 => 2.17-92+b1)   libc6-dev (2.17-92 => 2.17-92+b1)   libc6-i686 (2.17-92 => 2.17-92+b1)apt-cache policy libc6libc6:  Installed: 2.17-92  Candidate: 2.17-92+b1  Version table:     2.17-92+b1 0        500 http://ftp.us.debian.org/debian/ testing/main i386 Packages        500 http://http.debian.net/debian/ jessie/main i386 Packages *** 2.17-92 0        100 /var/lib/dpkg/statusapt-get changelog libc6eglibc (2.17-92) unstable; urgency=low  * kfreebsd/local-sysdeps.diff: update to revision 4839 (from glibc-bsd). -- Petr Salinger <petr.salinger@seznam.cz>  Wed, 31 Jul 2013 22:38:47 +0100eglibc (2.17-91) unstable; urgency=low  [ Petr Salinger ]  * switch libpthread implementation on kfreebsd-* to fbtl.    Closes: #703545. Closes: #665287. Closes: #683825. Closes: #489066.  * split some parts of kfreebsd/local-linuxthreads29.diff    into  kfreebsd/local-nscd-no-sockcloexec.diff and          kfreebsd/local-linuxthreads-tlsdesc.diff  * add kfreebsd/local-fbtl.diff and kfreebsd/local-fbtl-depends.diff  * kfreebsd/local-sysdeps.diff: update to revision 4809 (from glibc-bsd).    Closes: #718181. Addresses: #717032 in new binutils.  * update testsuite-checking/expected-results-*-kfreebsd-gnu-*    by fbtl tests that are known to fail.(snip)
What do '+b#' packages versions mean in Debian?
debian;package management
+bX means a binary non-maintainer upload. If you actually check the Debian changelog in the downloaded package (/usr/share/doc/package/changelog.Debian.gz or /changelog.Debian.arch.gz) it should show up there, and explain why it was needed.The Developer's Reference documents this in Recompilation or binary-only NMU.To save you the download:eglibc (2.17-92+b1) sid; urgency=low, binary-only=yes  * Binary-only non-maintainer upload for amd64; no source changes.  * Rebuild against libaudit1 -- amd64 Build Daemon (binet) <buildd-binet@buildd.debian.org>  Wed, 31 Jul 2013 22:38:47 +0100