问题
尝试更新存储库时出现以下错误，
avinash@avinash-VirtualBox:~$ sudo apt-get update
sudo: unable to stat /etc/sudoers: No such file or directory
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin
我意外地删除了/etc/sudoers文件，/etc/sudoers文件实际上属于sudo软件包，所以我尝试通过sudo重新安装pkexec，但它无法工作。
avinash@avinash-VirtualBox:~$ pkexec apt-get install sudo
Reading package lists... Done
Building dependency tree
Reading state information... Done
sudo is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 301 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue [Y/n]? y
Setting up sudo (1.8.6p3-0ubuntu3.1) ...
WARNING: /etc/sudoers not present!
chown: cannot access '/etc/sudoers': No such file or directory
dpkg: error processing sudo (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
sudo
E: Sub-process /usr/bin/dpkg returned an error code (1)
avinash@avinash-VirtualBox:~$
我也尝试过，
avinash@avinash-VirtualBox:~$ pkexec apt-get install --reinstall sudo
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 301 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
E: Internal Error, No file name for sudo:amd64
如何使sudo命令再次工作？
答案1
备份/etc/sudoers文件后：
sudo mv /etc/sudoers{,.bak}
如果你使用
pkexec apt-get install sudo
无法工作，因为apt-get将得到：
sudo is already the newest version.
如果使用：
pkexec apt-get install --reinstall sudo
也无法工作，因为找不到要删除的文件，并替换的/etc/sudoers文件。
但是，如果你使用：
pkexec apt-get purge sudo
pkexec apt-get install sudo
答案2
只需从Ubuntu live磁盘启动，并将/etc/sudoers文件复制到已安装的Ubuntu分区的/etc目录。
启动Ubuntu live 磁盘，并在启动时点击尝试Ubuntu选项。
运行sudo blkid命令了解已安装的Ubuntu分区id。
将已安装的Ubuntu分区挂载到一个特定的目录，
sudo mkdir /media/foo
sudo mount /dev/sdaX /media/foo # /dev/sdaX installed Ubuntu's partition id.
现在将live磁盘的sudoers文件复制到已安装Ubuntu分区的/etc目录。
sudo cp /etc/sudoers /media/foo/etc
现在从硬盘(启动你的Ubuntu操作系统)启动，它会工作，
答案3
以下是/etc/sudoers在Ubuntu 13.10上的原始内容：
#
# This file MUST be edited with the 'visudo' command as root.
#
# Please consider adding local content in /etc/sudoers.d/ instead of
# directly modifying this file.
#
# See the man page for details on how to write a sudoers file.
#
Defaults env_reset
Defaults mail_badpass
Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
# Host alias specification
# User alias specification
# Cmnd alias specification
# User privilege specification
root ALL=(ALL:ALL) ALL
# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL
# Allow members of group sudo to execute any command
%sudo ALL=(ALL:ALL) ALL
# See sudoers(5) for more information on"#include" directives:
#includedir /etc/sudoers.d
和权限：
-r--r----- 1 root root
chmod 440 /etc/sudoers和chown root:root /etc/sudoers
答案4
执行pkexec nano /etc/sudoers
然后粘贴
#
# This file MUST be edited with the 'visudo' command as root.
#
# Please consider adding local content in /etc/sudoers.d/ instead of
# directly modifying this file.
#
# See the man page for details on how to write a sudoers file.
#
Defaults env_reset
Defaults mail_badpass
Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
# Host alias specification
# User alias specification
# Cmnd alias specification
# User privilege specification
root ALL=(ALL:ALL) ALL
# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL
# Allow members of group sudo to execute any command
%sudo ALL=(ALL:ALL) ALL
# See sudoers(5) for more information on"#include" directives:
#includedir /etc/sudoers.d