Sudo (Українська)

Повʼязані статті

• Users and groups
• su
• doas

Sudo дозволяє системному адміністратору передавати різним користувачам чи групам користувачів повноваження запускати команди від імені користувача „root“ чи будь-якого іншого користувача. Окрім цього, команда веде часопис використаних команд та їх аргументів.

Інший спосіб запускати команди як root — su. От тільки, якщо su відкриває root консоль в якій можна вводити багато команд, то sudo дає право виконати лише одну команду. Завдяки цьому, зменшується ймовірність виконати команду з помилкою й поламати свою систему.

Із Sudo ще й можна запускати команди від імені інших користувачів. А використані команди та невдалі спроби отримати доступ записуються до журналу, для перевірки безпеки.

Встановлення

Встановіть пакунок sudo.

Використання

Перед використанням, sudo потрібно налагодити. Прочитайте #Налагодження.

Щоб скористатися sudo, просто додайте sudo поперед команди та її аргументів:

$ sudo команда

Наприклад, для pacman:

$ sudo pacman -Syu

Прочитайте sudo(8) щоб дізнатися більше.

Налагодження

Defaults skeleton

sudoers(5) § SUDOERS OPTIONS lists all the options that can be used with the Defaults command in the /etc/sudoers file.

See [1] for a list of options (parsed from the version 1.8.7 source code) in a format optimized for sudoers.

See sudoers(5) for more information, such as configuring the password timeout.

Переглянути наявні налаштування

Запустіть sudo -ll щоб вивести налаштування, прийняті на даний момент. Щоб дізнатися налаштування для певного користувача, запустіть sudo -lU ім'я_користувача.

Використання visudo

Налаштування для sudo знаходяться у файлі /etc/sudoers. Його можна редагувати тільки через команду visudo(8). Вона блокує оригінальний файл, створює тимчасову копію і перевіряє його на наявність помилок, переди тим як скопіювати його назад до /etc/sudoers.

Попередження:

• Ви зобов'язані написати sudoers без помилок! Будь-яка помилка зробить sudo непридатним для використання. Завжди використовуйте visudo щоб запобігти утворенню помилок.
• visudo(8) warns that configuring visudo to honor the user environment variables for their editor of choice may be a security hole, since it allows the user with visudo privileges to run arbitrary commands as root without logging simply by setting that variable to something else.

visudo використовує vi для редагування тексту. The sudo package is compiled with --with-env-editor and honors the use of the SUDO_EDITOR, VISUAL and EDITOR variables. EDITOR is not used when VISUAL is set.

To establish nano as the visudo editor for the duration of the current shell session, export EDITOR=nano; to use a different editor just once simply set the variable before calling visudo:

# EDITOR=nano visudo

Alternatively you may edit a copy of the /etc/sudoers file and check it using visudo -c /copy/of/sudoers. This might come in handy in case you want to circumvent locking the file with visudo.

To change the editor permanently, see Environment variables#Per user. To change the editor of choice permanently system-wide only for visudo, add the following to /etc/sudoers (assuming nano is your preferred editor):

# Reset environment by default
Defaults      env_reset
# Set default EDITOR to nano, and do not allow visudo to use EDITOR/VISUAL.
Defaults      editor=/usr/bin/nano, !env_editor

Example entries

To allow a user to gain full root privileges when they precede a command with sudo, add the following line:

USER_NAME   ALL=(ALL) ALL

To allow a user to run all commands as any user but only on the machine with hostname HOST_NAME:

USER_NAME   HOST_NAME=(ALL) ALL

To allow members of group wheel sudo access:

%wheel      ALL=(ALL) ALL

Tip: When creating new administrators, it is often desirable to enable sudo access for the wheel group and add the user to it, since by default Polkit treats the members of the wheel group as administrators. If the user is not a member of wheel, software using Polkit may ask to authenticate using the root password instead of the user password.

To disable asking for a password for user USER_NAME:

Warning: This will allow any process running with your user name to use sudo without asking for permission.

Defaults:USER_NAME      !authenticate

Enable explicitly defined commands only for user USER_NAME on host HOST_NAME:

USER_NAME HOST_NAME=/usr/bin/halt,/usr/bin/poweroff,/usr/bin/reboot,/usr/bin/pacman -Syu

Note: The most customized option should go at the end of the file, as the later lines overrides the previous ones. In particular such a line should be after the %wheel line if your user is in this group.

Enable explicitly defined commands only for user USER_NAME on host HOST_NAME without password:

USER_NAME HOST_NAME= NOPASSWD: /usr/bin/halt,/usr/bin/poweroff,/usr/bin/reboot,/usr/bin/pacman -Syu

A detailed sudoers example is available at /usr/share/doc/sudo/examples/sudoers. Otherwise, see the sudoers(5) for detailed information.

Sudoers default file permissions

The owner and group for the sudoers file must both be 0. The file permissions must be set to 0440. These permissions are set by default, but if you accidentally change them, they should be changed back immediately or sudo will fail.

# chown -c root:root /etc/sudoers
# chmod -c 0440 /etc/sudoers

Корисні поради

Вимкнути термін очікування при введенні паролю

Найдратівливіша ситуація: тривалий процес, що працює десь на тлі, із нормальними дозволами, та піднімається лише за потреби. В такому разі, він потребує паролю для sudo. Якщо його не помітити, то він застаріває й процес, в найкращому випадку, вилітає. Щоби справитись із цим, радимо вимкнути пароль для sudo або збільшити його термін очікування. Можна взагалі вимкнути термін очікування паролю, та як воно взагалі не підвищує рівень безпеки, для цього встановіть його рівним нулю:

Defaults passwd_timeout=0

Add terminal bell to the password prompt

To draw attention to a sudo prompt in a background terminal, users can simply make it echo a bell character:

Defaults passprompt="^G[sudo] password for %p: "

Note the ^G is a literal bell character. E.g. in vim, insert using the sequence Ctrl+v Ctrl+g, or in nano, Alt+v Ctrl+g.

Passing aliases

If you use a lot of aliases, you might have noticed that they do not carry over to the root account when using sudo. However, there is an easy way to make them work. Simply add the following to your ~/.bashrc or /etc/bash.bashrc:

alias sudo='sudo '

Disable per-terminal sudo

Warning: This will let any process use your sudo session.

If you are annoyed by sudo's defaults that require you to enter your password every time you open a new terminal, set timestamp_type to global:

Defaults timestamp_type=global

Reduce the number of times you have to type a password

If you are annoyed that you have to re-enter your password every 5 minutes (default), you can change this by setting a longer value for timestamp_timeout (in minutes):

Defaults timestamp_timeout=10

If you are using a lot of sudo commands on a row, it is more logical to refresh the timeout every time you use sudo than to increase timestamp_timeout. Refreshing the timeout can be done with sudo -v (whereas sudo -K revokes immediately).

You might want to automate this by adding the following to your .bashrc:

alias sudo='sudo -v; sudo '

It is also possible to use a bash function; for more details see stackexchange.

Environment variables

If you have a lot of environment variables, or you export your proxy settings via export http_proxy="...", when using sudo these variables do not get passed to the root account unless you run sudo with the -E option.

$ sudo -E pacman -Syu

The recommended way of preserving environment variables is to append them to env_keep:

/etc/sudoers

Defaults env_keep += "ftp_proxy http_proxy https_proxy no_proxy"

Root password

Users can configure sudo to ask for the root password instead of the user password by adding targetpw (target user, defaults to root) or rootpw to the Defaults line in /etc/sudoers:

Defaults targetpw

To prevent exposing your root password to users, you can restrict this to a specific group:

Defaults:%wheel targetpw
%wheel ALL=(ALL) ALL

Disable root login

Users may wish to disable the root login. Without root, attackers must first guess a user name configured as a sudoer as well as the user password. See for example OpenSSH#Deny.

Warning:

• Be careful, you may lock yourself out by disabling root login. Sudo is not automatically installed and its default configuration allows neither passwordless root access nor root access with your own password. Ensure a user is properly configured as a sudoer before disabling the root account!
• If you have changed your sudoers file to use rootpw as default, then do not disable root login with any of the following commands!
• If you are already locked out, see Password recovery for help.

The account can be locked via passwd:

# passwd -l root

A similar command unlocks root.

$ sudo passwd -u root

Alternatively, edit /etc/shadow and replace the root's encrypted password with "!":

root:!:12345::::::

To enable root login again:

$ sudo passwd root

Tip: To get to an interactive root prompt, even after disabling the root account, use sudo -i.

kdesu

kdesu may be used under KDE to launch GUI applications with root privileges. It is possible that by default kdesu will try to use su even if the root account is disabled. Fortunately one can tell kdesu to use sudo instead of su. Create/edit the file ~/.config/kdesurc:

[super-user-command]
super-user-command=sudo

or use the following command:

$ kwriteconfig5 --file kdesurc --group super-user-command --key super-user-command sudo

Harden with sudo example

Let us say you create 3 users: admin, devel, and joe. The user "admin" is used for journalctl, systemctl, mount, kill, and iptables; "devel" is used for installing packages, and editing config files; and "joe" is the user you log in with. To let "joe" reboot, shutdown, and use netctl we would do the following:

Edit /etc/pam.d/su and /etc/pam.d/su-l. Require user be in the wheel group, but do not put anyone in it.

#%PAM-1.0
auth            sufficient      pam_rootok.so
# Uncomment the following line to implicitly trust users in the "wheel" group.
#auth           sufficient      pam_wheel.so trust use_uid
# Uncomment the following line to require a user to be in the "wheel" group.
auth            required        pam_wheel.so use_uid
auth            required        pam_unix.so
account         required        pam_unix.so
session         required        pam_unix.so

Limit SSH login to the 'ssh' group. Only "joe" will be part of this group.

# groupadd -r ssh
# gpasswd -a joe ssh
# echo 'AllowGroups ssh' >> /etc/ssh/sshd_config

Restart sshd.service.

Add users to other groups.

1. for g in power network ;do ;gpasswd -a joe $g ;done

# for g in network power storage ;do ;gpasswd -a admin $g ;done

Set permissions on configs so devel can edit them.

# chown -R devel:root /etc/{http,openvpn,cups,zsh,vim,screenrc}

Cmnd_Alias  POWER       =   /usr/bin/shutdown -h now, /usr/bin/halt, /usr/bin/poweroff, /usr/bin/reboot
Cmnd_Alias  STORAGE     =   /usr/bin/mount -o nosuid\,nodev\,noexec, /usr/bin/umount
Cmnd_Alias  SYSTEMD     =   /usr/bin/journalctl, /usr/bin/systemctl
Cmnd_Alias  KILL        =   /usr/bin/kill, /usr/bin/killall
Cmnd_Alias  PKGMAN      =   /usr/bin/pacman
Cmnd_Alias  NETWORK     =   /usr/bin/netctl
Cmnd_Alias  FIREWALL    =   /usr/bin/iptables, /usr/bin/ip6tables
Cmnd_Alias  SHELL       =   /usr/bin/zsh, /usr/bin/bash
%power      ALL         =   (root)  NOPASSWD: POWER
%network    ALL         =   (root)  NETWORK
%storage    ALL         =   (root)  STORAGE
root        ALL         =   (ALL)   ALL
admin       ALL         =   (root)  SYSTEMD, KILL, FIREWALL
devel	    ALL         =   (root)  PKGMAN
joe	    ALL         =   (devel) SHELL, (admin) SHELL 

With this setup, you will almost never need to login as the Root user.

"joe" can connect to his home WiFi.

$ sudo netctl start home
$ sudo poweroff

"joe" can not use netctl as any other user.

$ sudo -u admin -- netctl start home

When "joe" needs to use journalctl or kill run away process he can switch to that user.

$ sudo -i -u devel
$ sudo -i -u admin

But "joe" cannot switch to the root user.

$ sudo -i -u root

If "joe" want to start a gnu-screen session as admin he can do it like this:

$ sudo -i -u admin
[admin]$ chown admin:tty `echo $TTY`
[admin]$ screen

Configure sudo using drop-in files in /etc/sudoers.d

sudo parses files contained in the directory /etc/sudoers.d/. This means that instead of editing /etc/sudoers, you can change settings in standalone files and drop them in that directory. This has two advantages:

• There is no need to edit a sudoers.pacnew file;
• If there is a problem with a new entry, you can remove the offending file instead of editing /etc/sudoers (but see the warning below).

The format for entries in these drop-in files is the same as for /etc/sudoers itself. To edit them directly, use visudo -f /etc/sudoers.d/somefile. See sudoers(5) § Including other files from within sudoers for details.

The files in /etc/sudoers.d/ directory are parsed in lexicographical order, file names containing . or ~ are skipped. To avoid sorting problems, the file names should begin with two digits, e.g. 01_foo.

Note: The order of entries in the drop-in files is important: make sure that the statements do not override themselves.

Warning: The files in /etc/sudoers.d/ are just as fragile as /etc/sudoers itself: any improperly formatted file will prevent sudo from working. Hence, for the same reason it is strongly advised to use visudo

Editing files

sudo -e or sudoedit lets you edit a file as another user while still running the text editor as your user.

This is especially useful for editing files as root without elevating the privilege of your text editor, for more details read sudo(8) § e.

Note that you can set the editor to any program, so for example one can use meld to manage pacnew files:

$ SUDO_EDITOR=meld sudo -e /etc/file{,.pacnew}

Увімкнути образи

Ви можете увімкнути образи в sudo. Для цього додайте цей рядок до файлу sudoers з visudo:

/etc/sudoers

Defaults insults

Якщо ви введете хибний пароль, то замість Upon entering an incorrect password this will replace слід вказати пароль sudo буде писати різні кумедні образи.

Troubleshooting

SSH problem without TTY

SSH does not allocate a tty by default when running a remote command. Without an allocated tty, sudo cannot prevent the password from being displayed. You can use ssh's -t option to force it to allocate a tty.

The Defaults option requiretty only allows the user to run sudo if they have a tty.

# Disable "ssh hostname sudo <cmd>", because it will show the password in clear text. You have to run "ssh -t hostname sudo <cmd>".
#
#Defaults    requiretty

Permissive umask

Sudo will union the user's umask value with its own umask (which defaults to 0022). This prevents sudo from creating files with more open permissions than the user's umask allows. While this is a sane default if no custom umask is in use, this can lead to situations where a utility run by sudo may create files with different permissions than if run by root directly. If errors arise from this, sudo provides a means to fix the umask, even if the desired umask is more permissive than the umask that the user has specified. Adding this (using visudo) will override sudo's default behavior:

Defaults umask = 0022
Defaults umask_override

This sets sudo's umask to root's default umask (0022) and overrides the default behavior, always using the indicated umask regardless of what umask the user as set.