dpkg -x解压deb的时候得注意点

周四晚上弄trac，下了个deb包想解压看个东西，然后顺手 dpkg -x foobar.deb /tmp

周五上班，gdm能起来，输入用户名和密码，系统就是进不去。

查了半天才发现是 /tmp 目录的权限被修改成了 755，导致普通用户不能往/tmp目录写东西，当然gnome/scim都启不动了。

想想原因在哪，原因就在于我用dpkg -x 解deb的时候把数据解压到/tmp目录，而dpkg -x会自动将解压目标目录的根目录权限修改为755。

搜索了一下，找到原因了。在 debian 的邮件列表里有人在说此事，一看是98年的邮件。。

You did "dpkg -x dpkg.deb /tmp" didn't you? That's what broke your /tmp
permissions, you need to make a subdirectory to extract into, the root of
the directory you extract the package into has its permissions changed.
This is "not a bug but a feature"

If you extract a tar archive into /tmp itself (and not a subdirectory),
the permissions may well change. The tar archive contains an entry
for the root directory of the archive, including permissions for it,
so your /tmp inherits those permissions. Make a subdirectory and
extract into there.