This happened a few times. So I am curious why.

For some purpose, I did tar cf /backup/os.tar / --one-file-system. Then booted into rescue system and remade root filesystem. Then tar xf /backup/os.tar. And sendmail could not work. Either was lightdm and unity.

Watched various logs for a day, I figured out the root cause. All was because of permission was changed for some files. For example, /usr/lib/dbus-1.0/dbus-daemon-launch-helper was not executable. /var/lib/sendmail/ belongs to wrong group.


Simply add -p in your tar command.

-p, --preserve-permissions, --same-permissions
                             extract information about file permissions
                             (default for superuser)
  • So I am confused. I ran my command with sudo, I thought that applied "default for superuser". – Magicloud Dec 19 '15 at 10:48
  • Yes, you must use sudo for your tar command. – Tung Tran Dec 19 '15 at 12:14

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