I use strace to see why apt-get update is too slow, finally I found apt-get loop 3~n to '(? , F_SETFD, FD_CLOEXEC) = 0' ubuntu 14.04 root@dev2:/tmp/apt-1.0.1ubuntu2.1# apt-cache show apt Package: apt Priority: important Section: admin Installed-Size: 3576 Maintainer: Ubuntu Developers