PGP(Pretty Good Privay)是一套用于数据加密、解密和数据签名生成、验证的软件。它由一系列散列、数据压缩、对称密钥加密和公钥加密算法组成。每种功能提供几种算法可供选择。



GnuPG(Gnu Privacy Guard)是以GPL许可协议发行的,免费、开源、完整的PGP替代软件,遵从OpenPGP标准(RFC 4880)。
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A Dummie’s Guide to Flashing Factory Firmware on Nexus 7 [2013]

This guide aims to teach people with basic computer skills to flash factory firmware image on Nexus 7 [2013] using Windows 7/10. It should apply to other modern stock Android devices.

Note: To prevent unauthorized access, unlocking the bootloader will delete all personal data on the device. Therefore, you must backup important data first before proceeding with the following procedure.
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Keeping track of svn repositories using git

  • Clone an svn repository with entire history.
  • git svn clone --prefix=origin/ svn://

    Note: This can be very time-consuming on a large svn repository, esp. when the network connectivity is poor.

  • Clone an svn repository with recent history only.
  • git svn clone --prefix=origin/ -r 28015:HEAD svn://

  • When cloning fails on a large repository, keep fetching until it’s done.
  • cd DD-WRT
    while ! git svn fetch; do sleep 10; done

  • Fetch unfetched commits from the svn repository and rebase current work against it.
  • git svn rebase

  • Checkout an older svn revision.
  • git checkout `git svn find-rev r28015`

  • Return to the latest revision.
  • git checkout master

  • Remove untracked files in the current directory.
  • git clean -n
    git clean -f

Removing alternative Ubuntu flavors completely

When Ubuntu users want to try other Ubuntu flavors, e.g. Xubuntu and Lubuntu, they usually just install their meta packages:

$ sudo apt-get install xubuntu-desktop


$ sudo apt-get install lubuntu-desktop

apt-get can install their dependencies automatically. However, when users want to remove the alternative Ubuntu flavors completely, they are out of luck, because inter-dependencies among many packages can be rather complex, and apt tools simply does not automatically remove the dependencies of meta packages.
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Upgrading Ubuntu 12.04 to 14.04 on Pentium-M computers

Starting from 12.10, Ubuntu no longer offered non-PAE kernels. Some Pentium-M processors do not announce the PAE flag, although they actually have the PAE capability. When doing a release upgrade from 12.04, the Ubuntu release upgrade tool will complain of missing PAE feature on such computers and then abort after printing a link to the EnablingPAE document on the Ubuntu community help website. However, this document only covers fresh Ubuntu installation on such computers, leaving release upgrade users out in the cold.
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