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在linux中(和大部分unix系统), 有一个超级用户叫做root. 类似于window系统的 Administrator. 这个超级用户可以作任何事情, 但是使用这个超级用户做日常的工作是很危险的. 你可以输入一个错误的命令,摧毁系统. 理想的方式,你使用的帐户仅有处理手边任务的权限. 在一写情况下, 需要使用 root, 但是在大多数时候仅仅普通用户就够了. 默认情况下, root帐户的密码是被锁定的在ubuntu中. 这就意味着你不能直接使用root帐户登陆 或者使用su名名成为 root 用户, 但是, 既然root帐户是实际存在的,任然可以以root权限来运行程序.这就是 sudo 由来; 它允许授权的用户 (通常是管理员用户组; 更多的信息参考AddUsersHowto) 运行程序而不用知道root帐户的密码. 这就意味着你的使用 sudo 在那些需要root权限的命令; 仅仅是在那些命令前加"sudo". 更多广泛的使用范例, 请看下面. 同样的, 当你运行那些需要root权限的图形界面程序 (例如网络配置小程序), 你也将被提示输入密码. 记住, 当sudo 要求输入密码, 它要的是 你的用户密码, 而不是root的密码.
The benefits of leaving root logins disabled by default include the following:
- The installer has to ask fewer questions.
- Users don't have to remember an extra password (i.e. the root password), which they are likely to forget.
- It avoids the "I can do anything" interactive login by default (e.g. the tendency by users to login as an "Administrator" user in Microsoft Windows systems), you will be prompted for a password before major changes can happen, which should make you think about the consequences of what you are doing.
- Sudo adds a log entry of the command(s) run (In
/var/log/auth.log). If you mess up, you can always go back and see what commands were run. It is also nice for auditing.
- Every cracker trying to brute-force their way into your box will know it has an account named root and will try that first. What they don't know is what the usernames of your other users are. Since the root account password is locked, this attack becomes essentially meaningless, since there is no password to crack or guess in the first place.
- Allows easy transfer for admin rights, in a short term or long term period, by adding and removing users from groups, while not compromising the root account.
- sudo can be setup with a much more fine-grained security policy.
- The authentication automatically expires after a short time (which can be set to as little as desired or 0); so if you walk away from the terminal after running commands as root using sudo, you will not be leaving a root terminal open indefinitely.
sudo chown bob:bob /home/bob/*
sudo /etc/init.d/networking restart
- 密码默认会保存十五分钟. 在那之后, 你需要重新输入密码（在需要的情况下）.
- 你的密码l 不会 在屏幕上显示当你输入的时候, 甚至不会显示一行星号(******). 它将被输入在按下按键时!
sudo !!将会最后一次输入的命令, 除非在它前面使用sudo.
- 你应该 从不 使用sudo以root启动图形界面应用程序. 应该i使用
gksudo来运行这些程序 (例如 ALT+F2 gksudo gedit).
- 要运行图形配置工具, 之需要通过菜单启动即可.
To add a new user to sudo, open the Users and Groups tool from
System --> Administration menu. Then click on the user and then on properties. Choose the User Privileges tab. In the tab, find Executing system administration tasks and check that.
/!\ In the terminal this would be:
sudo adduser $user admin, where you replace $user with the name of the user.
Logging in as another user
- To login as another user.
NB Please don't use this to become root, please see the bottom of the page for some more information.
sudo -i -u username
For example to become amanda for tape management purposes.
sudo -i -u amanda
The password being asked for is your own.
Downsides of using sudo
Although for desktops the benefits of using sudo are great, there are possible issues which need to be noted:
- Redirecting the output of commands run with sudo requires a different approach. For instance consider
sudo ls > /root/somefilewill not work since it is the shell that tries to write to that file. You can use `ls | sudo tee -a /root/somefile` to append, or `ls | sudo tee /root/somefile` to overwrite contents. You could also pass the whole command to a shell process run under sudo to have the file written to with root permissions, such as `sudo bash -c "ls > /root/somefile"`.
- In a lot of office environments the ONLY local user on a system is root. All other users are imported using NSS techniques such as nss-ldap. To setup a workstation, or fix it, in the case of a network failure where nss-ldap is broken, root is required. This tends to leave the system unusable unless cracked. An extra local user, or an enabled root password is needed here.
- Isn't sudo less secure than su?
The basic security model is the same, and therefore these two systems share their primary weaknesses. Any user who uses `su` or `sudo` must be considered to be a privileged user. If that user's account is compromised by an attacker, the attacker can also gain root privileges the next time the user does so. The user account is the weak link in this chain, and so must be protected with the same care as root. On a more esoteric level, `sudo` provides some features which encourage different work habits, which can positively impact the security of the system. `sudo` is commonly used to execute only a single command, while `su` is generally used to open a shell and execute multiple commands. The `sudo` approach reduces the likelihood of a root shell being left open indefinitely, and encourages the user to minimize their use of root privileges.
- I won't be able to enter single-user mode!
The sulogin program in Ubuntu is patched to handle the default case of a locked root password.
- I can get a root shell from the console without entering a password!
You have to enter your password. Console users have access to the boot loader, and can gain administrative privileges in various ways during the boot process. For example, by specifying an alternate `init(8)` program. Linux systems are not typically configured to be secure at the console, and additional steps (for example, setting a root password, a boot loader password and a BIOS password) are necessary in order to make them so. Note that console users usually have physical access to the machine and so can manipulate it in other ways as well.
Re-disabling your root account
If for some reason you have enabled your root account and wish to disable it again, open a terminal and issue the following command:
sudo passwd -l root
Enabling the root account
<!> Enabling the root account is neither supported nor necessary.
Anything you need to do as administrator of an Ubuntu system can be done via sudo or gksudo. If you really need a persistent root login, use
sudo -i. Logging in to X as root is most likely to cause very serious trouble. If you believe you need a root account to perform a certain action, please consult the official support channels first, to make sure there is not a better alternative.
Drag & Drop Sudo
gksudo "gnome-open %u"
When you drag and drop any file on this launcher (it's useful to put it on the desktop or on a panel), it will be opened as root with its own associated application. This is helpful especially when you're editing config files owned by root, since they will be opened as read only by default with gedit, etc.
Special notes on sudo and shells
- None of the methods below are suggested or supported by the designers of Ubuntu.
- Please do not suggest this to others unless you personally are available 24/7 to support the user if they have issues as a result of running a shell as root.
- To start a root shell (i.e. a command window where you can run root commands), starting root's environment and login scripts, use:
sudo -i (equivalent to sudo su - , gives you roots environment configuration)
- To start a root shell, but keep the current shell's environment, use:
sudo -s (equivalent to sudo su)