需求：

前一段时间有收到这样的一个关于linux用户的权限相关的需求，在centos上给用户创建一个用SSH的密钥访问服务器，另给该用户添加到root权限组。记录下了步骤，分享给大家。

步骤：

添加root用户组：

groupadd ams

给用户组添加root权限，且切换root不需要输入root密码，权限高，请注意

$ visudo  
## 添加了这一行 %ams    ALL=(ALL)       NOPASSWD: ALL## Sudoers allows particular users to run various commands as
## the root user, without needing the root password.
##
## Examples are provided at the bottom of the file for collections
## of related commands, which can then be delegated out to particular
## users or groups.
##
## This file must be edited with the 'visudo' command.## Host Aliases
## Groups of machines. You may prefer to use hostnames (perhaps using
## wildcards for entire domains) or IP addresses instead.
# Host_Alias     FILESERVERS = fs1, fs2
# Host_Alias     MAILSERVERS = smtp, smtp2## User Aliases
## These aren't often necessary, as you can use regular groups
## (ie, from files, LDAP, NIS, etc) in this file - just use %groupname
## rather than USERALIAS
# User_Alias ADMINS = jsmith, mikem## Command Aliases
## These are groups of related commands...## Networking
# Cmnd_Alias NETWORKING = /sbin/route, /sbin/ifconfig, /bin/ping, /sbin/dhclient, /usr/bin/net, /sbin/iptables, /usr/bin/rfcomm, /usr/bin/wvdial, /sbin/iwconfig, /sbin/mii-tool## Installation and management of software
# Cmnd_Alias SOFTWARE = /bin/rpm, /usr/bin/up2date, /usr/bin/yum## Services## Updating the locate database
# Cmnd_Alias LOCATE = /usr/bin/updatedb## Storage
# Cmnd_Alias STORAGE = /sbin/fdisk, /sbin/sfdisk, /sbin/parted, /sbin/partprobe, /bin/mount, /bin/umount## Delegating permissions
# Cmnd_Alias DELEGATING = /usr/sbin/visudo, /bin/chown, /bin/chmod, /bin/chgrp## Processes
# Cmnd_Alias PROCESSES = /bin/nice, /bin/kill, /usr/bin/kill, /usr/bin/killall## Drivers
# Cmnd_Alias DRIVERS = /sbin/modprobe# Defaults specification#
# Refuse to run if unable to disable echo on the tty.
#
Defaults   !visiblepw#
# Preserving HOME has security implications since many programs
# use it when searching for configuration files. Note that HOME
# is already set when the the env_reset option is enabled, so
# this option is only effective for configurations where either
# env_reset is disabled or HOME is present in the env_keep list.
#
Defaults    always_set_home
Defaults    match_group_by_gid# Prior to version 1.8.15, groups listed in sudoers that were not
# found in the system group database were passed to the group
# plugin, if any. Starting with 1.8.15, only groups of the form
# %:group are resolved via the group plugin by default.
# We enable always_query_group_plugin to restore old behavior.
# Disable this option for new behavior.
Defaults    always_query_group_pluginDefaults    env_reset
Defaults    env_keep =  "COLORS DISPLAY HOSTNAME HISTSIZE KDEDIR LS_COLORS"
Defaults    env_keep += "MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS LC_CTYPE"
Defaults    env_keep += "LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGES"
Defaults    env_keep += "LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE"
Defaults    env_keep += "LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET XAUTHORITY"#
# Adding HOME to env_keep may enable a user to run unrestricted
# commands via sudo.
#
# Defaults   env_keep += "HOME"Defaults    secure_path = /sbin:/bin:/usr/sbin:/usr/bin## Next comes the main part: which users can run what software on
## which machines (the sudoers file can be shared between multiple
## systems).
## Syntax:
##
##      user    MACHINE=COMMANDS
##
## The COMMANDS section may have other options added to it.
##
## Allow root to run any commands anywhere
root    ALL=(ALL)       ALL## Allows members of the 'sys' group to run networking, software,
## service management apps and more.
# %sys ALL = NETWORKING, SOFTWARE, SERVICES, STORAGE, DELEGATING, PROCESSES, LOCATE, DRIVERS## Allows people in group wheel to run all commands
%wheel  ALL=(ALL)       ALL## Same thing without a password
# %wheel        ALL=(ALL)       NOPASSWD: ALL
%ams    ALL=(ALL)       NOPASSWD: ALL## Allows members of the users group to mount and unmount the
## cdrom as root
# %users  ALL=/sbin/mount /mnt/cdrom, /sbin/umount /mnt/cdrom## Allows members of the users group to shutdown this system
# %users  localhost=/sbin/shutdown -h now## Read drop-in files from /etc/sudoers.d (the # here does not mean a comment)
#includedir /etc/sudoers.d

添加用户：

useradd <用户名>

将用户添加到root用户组：

usermod -a -G ams <用户名>

给用户创建家目录：

mkdir -p /home/<用户名>/.ssh/

给用户创建authorized_keys文件：

touch /home/<用户名>/.ssh/authorized_keys

添加用户的公钥到authorized_keys中：

echo "ssh-rsa AAAAB3NzaC1yc2.....59AHv6osqY1ZuMrnl7Q== example@example.com" >> /home/<用户名>/.ssh/authorized_keys