帳號管理

登入失敗後鎖定帳號

RedHat 8

NOTE:

新增目錄 faillock (optional)

TIP: 如果不指定目錄，預設目錄是 /var/run/faillock。

mkdir /var/log/faillock

Edit /etc/pam.d/system-auth , /etc/pam.d/password-auth

# for auth
# faillock, add the below line BEFORE pam_unix.so
auth required pam_faillock.so preauth dir=/var/log/faillock silent audit deny=3 fail_interval=900 unlock_time=600
auth required pam_faillock.so authfail dir=/var/log/faillock unlock_time=600
#

auth        sufficient    pam_unix.so try_first_pass nullok

# faillock, add the below line AFTER pam_unix.so
auth        [default=die] pam_faillock.so authfail deny=3 fail_interval=900 unlock_time=600
#

# for account
# faillock, add the below line BEFORE pam_unix.so
account required pam_faillock.so
#

account     required      pam_unix.so

 

RedHat 6

Edit /etc/pam.d/system-auth , /etc/pam.d/password-auth

# for auth
# add the below line BEFORE pam_unix.so
auth required pam_faillock.so preauth silent audit deny=3 unlock_time=600  # insert this

auth        sufficient    pam_unix.so nullok try_first_pass

# add the below line AFTER pam_unix.so
auth [default=die] pam_faillock.so authfail audit deny=3 unlock_time=600  # insert this

# for account
# add the below line BEFORE pam_unix.so
account required pam_faillock.so  # insert this

account     required      pam_unix.so

預設不會套用在 root；如果需要限制 root，下面這一行加上 even_deny_root ：

auth    required    pam_faillock.so preauth silent audit deny=3 even_deny_root unlock_time=1200 root_unlock_time=600

如果要排除特定 user，在第一個 pam_faillock.so 之前加上這行:

auth [success=1 default=ignore] pam_succeed_if.so user in user1:user2:user3

如何手動解鎖與檢查被鎖定的帳戶

# display the authentication failure for all users 
faillock

# display the authentication failure for the specified user
faillock --user mytest

# unlock the user
faillock --user mytest --reset

Tip:

要確認設定是否有作用，可以監看 log 檔 /var/log/secure，登入錯誤次數達到設定值時，應該要出現下面的訊息。

Mar 8 15:26:08 centos7 sshd[26995]: pam_faillock(sshd:auth): Consecutive login failures for user i04181 account temporarily locked

VSFTPD

如果 vsftpd 使用系統帳號做認證時，也適用帳號鎖定的規則。

參考教學




進階管理技巧

建立系統用帳號

CentOS/RedHat)

groupadd -r asterisk
useradd -r -g asterisk -d /var/lib/asterisk -M asterisk

Ubuntu/Debian)

addgroup --system asterisk
adduser --system --ingroup asterisk --home /var/lib/asterisk --no-create-home --shell /bin/bash asterisk
變更帳號為管理者權限
# Debian/Ubuntu
# Add the user into the group sudo
sudo usermod -aG sudo <user-name>
# Verify the user's groups
groups <user-name>
強制修改密碼

強迫使用者在第一次登入後，修改他們的登入密碼

# 先將帳號鎖定
usermod -L <username>

# 強制第一次登入必須修改密碼
# 套用後，原密碼會立即過期，直到完成密碼變更。
chage -d 0 <username>

# 解除帳號鎖定
usermod -U <username>

# 檢查帳號的期限
chage -l <user-name>
帳號使用期限
# 檢查帳號期限
chage -l <user-name>

# 設定有效期限 
chage -M 10 <user-name>             # 10 天後密碼即失效
chage -E "2017-02-20" <user-name>   # 2017-02-20 以後帳號即鎖定
chage -I 10 <user-name>             # 如有設定密碼期限時，當密碼失效起 10 日後自動鎖定帳號 

# 解除期限
chage -E -1 <user-name>       ; 數字 -1 解除期限設定
帳號鎖定與解鎖
# 鎖定帳號
usermod -L <user-name>
passwd -l <user-name>
chage -E 0 <user-name>

# 解鎖帳號
usermod -U <user-name>
passwd -u <user-name>
chage -E <user-name>

# 檢查帳號鎖定狀態
grep <user-name> /etc/shadow

dbtest:!$6$hFCW6eI1$kI9J9QrxCjnpvzFPJnxSpNvQ...  密碼欄有 ! 符號表示鎖定

# List the locked and passwordless accounts
getent shadow | awk '/^.*:[!\*].*/' | cut -d: -f1
TIPs:
注意：passwd 雖然可以鎖定帳號，但仍可以用 SSH-Key 登入。

登入失敗的自動鎖定：

RHEL 7

# To enable the faillock
# unlock_time: seconds
authconfig --enablefaillock --faillockargs="deny=5 unlock_time=1200" --update

# To disable the faillock
authconfig --disablefaillock --update

# Validate the configuration
authconfig --test

# Check the login attempts failed
faillock

# Unlock the user locked immediately
faillock --user test01 --reset

修改既有帳號的設定
# 修改註解
usermod -c "John" john
# 修改 shell
usermod -s "/sbin/nologin" alang
# 修改帳號名稱
usermod -l newuser currentuser
限制某帳號不可遠端登入

但可以由其他允許帳號從遠端登入後，執行 su 切換到該帳號

情境：限制 devrpt 可以從遠端登入，但其他帳號在登入後可以 su 到 devrpt。

方法一: 修改 sshd_config

# Added by Alang
# prevent certain users from using ssh for login
# while retaining the option to 'su username'
#
DenyUsers istdc

方法二: 最快速且容易設定但不適用需要有密碼的帳號

# 刪除 devrpt 的密碼
passwd -d devrpt

方法三: 比較嚴謹的做法

以 CentOS 為例：

1. 編輯 /etc/security/access.conf，加上這幾行

# The line 'cron crond' is required
+:devrpt:cron crond tty1 tty2 tty3 tty4 tty5 tty6
-:devrpt:ALL

TIPs：
內容格式為 permission : username: origins

permission + 允許 或 - 拒絕
username 帳號
origins 來源，這可以是 tty 名稱'、主機/網域名稱、IP 。

注意：在此例，必須加上 cron crond 這一行，否則該帳號的 crontab 會無法工作。

2. 對於不同的登入服務，需要修改相應的安全設定檔

視需要將以下內容加入其中一項或多項檔案內

# Limited users for remote login via telnet
# Check the file /etc/security/access.conf
account    required     pam_access.so
重建帳號的家目錄
mkhomedir_helper <username>
限制登入後的行為

情境: 帳號執行遠端登入後，只能變更密碼與幾個受限制的指令權限

RedHat-KB: https://access.redhat.com/solutions/65822

# Create the restricted shell
cp /bin/bash /bin/rbash

# Create a directory that is used as the HOME of the user
mkdir /home/dbuser/
mkdir /home/dbuser/bin

# Modify the target user 'siview' for the shell as restricted shell
usermod -d /home/dbuser -s /bin/rbash siview
# or for new user
useradd -d /home/dbuser -s /bin/rbash siview

If a user uses rbash, the user can not do the following after login:

# Create specific profile for the user
vi /home/dbuser/.bash_profile

.bash_profile:

# cat /home/localuser/.bash_profile  
# .bash_profile  

# Get the aliases and functions  
if [ -f ~/.bashrc ]; then  
. ~/.bashrc  
fi  
# User specific environment and startup programs  
PATH=$HOME/bin  
export PATH
# Create the softlinks of commands which are required for the user
ln -s /bin/date /home/dbuser/bin/
ln -s /bin/ls /home/dbuser/bin/
ln -s /usr/bin/passwd /home/dbuser/bin/
密碼強度

預設強度:

Edit /etc/pam.d/system-auth , /etc/pam.d/password-auth

CentOS 5/6)

NOTE: CentOS 5 沒有 /etc/pam.d/password-auth , 所以只需要設定 /etc/pam.d/system-auth
# Set password strength
#password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    requisite     pam_cracklib.so minlen=8 dcredit=-1 ucredit=-1 lcredit=-1

CentOS 7/8)

Edit /etc/security/pwquality.conf

# Set password strength
minlen = 8
dcredit = -1
ucredit = -1
lcredit = -1

預設 root 不會套用密碼強度規則，如果要做限制，編輯 /etc/pam.d/system-auth 與 /etc/pam.d/password-auth ，在 password 這一行加上 enforce_for_root。

# Enforce root for password strength
password    requisite     pam_pwquality.so try_first_pass local_users_only retry=3 authtok_type= enforce_for_root

記住幾代密碼

Edit /etc/pam.d/system-auth , /etc/pam.d/password-auth
CentOS 5/6)

# Keep history of passwords used
# Add remember=N
# The last n passwords for each user are saved in /etc/security/opasswd in order to force password change history 
# and keep the user from alternating between the same password too frequently.
#password    sufficient    pam_unix.so sha512 shadow nullok try_first_pass use_authtok
password    sufficient    pam_unix.so sha512 remember=8 shadow nullok try_first_pass use_authtok

CentOS 7/8)

# Keep history of passwords used, insert the below line after pam_pwquality.so line
password    requisite     pam_pwhistory.so remember=8 use_authtok
TIP: 歷史密碼會被儲存在 /etc/security/opasswd .
群組管理
# Create a new group
groupadd <group-name>
addgroup <group-name>

# add a group into an account
usermod -aG mygroup user1
useradd -aG family,friends james

# To change the primary group of the user tom to family
usermod -g family tom

# remove user from a group
gpasswd -d user1 mygroup

# list all users in a group
lid -g mygroup

# list groups for current user
groups

# List groups for specified user
groups username
指令 passwd
# displays the status of user account password settings
# [Username] [Status] [Date Last Changed] [Min. Age] [Max. Age] [Warn. Period] [ Inactivity Period]
# Status: 
#  - P: Usable password
#  - NP: No password
#  - L: Locked password
# Age: 
#  - 99999: Never expires
#  - 0: Can be changed at anytime
#  - -1: Disabled
passwd -S evans
 evans PS 2020-09-07 0 99999 7 -1 (Password set, SHA512 crypt.)

# Check password status for all accounts
passwd -Sa

# lock the password of a specified account
passwd -l user1

# unlock the password
passwd -u user2

# delete a password for an account
passwd -d user1

# expire a password for an account
# This will force user to change the password at next login.
passwd -e user2

# This sets the number of days before a password can be changed. 
# By default, a value of zero is set, which indicates that the user may change 
# their password at any time.
# This means user2 cannot change its own password until 10 days have passed.
passwd -n 10 user2

# To confirm the password setting made with the -n option above, run the following command:
# The value of 10 after the date indicates the minimum number of days 
# until the password can be changed.
passwd -S user1
user1 PS 2020-12-04 10 99999 7 -1 (Password set, SHA512 crypt.)

# This means after 90 days, the password is required to be changed.
passwd -x 90 user2

# This means the user will receive warnings that the password will expire 7 days 
# before the expiration.
passwd -w 7 user2

# This means after a user account has had an expired password for 5 days, 
# the user may no longer sign on to the account.
passwd -i 5 user2

# This command will read from the echo command and pass it to the passwd command. 
# So this will set the user1 password to userpasswd1.
echo "userpasswd1"|passwd --stdin user1
指令 getent
# List all user
getent passwd
getent passwd | awk -F: '{print $1}'

# List a specified user
getent passwd <username>

# List the locked and no-login accounts
getent shadow | awk '/^.*:[!\*].*/' | cut -d: -f1

# List the users with uid between 1000 ~ 1500
getent passwd {1000..1500}

批次建立多個帳號
# Step 1 – Create an encrypted password
## perl one liner ##
#perl -e 'print crypt("Your-Clear-Text-Password-Here", "salt"),"\n"'

password="1YelloDog@"
pass=$(perl -e 'print crypt($ARGV[0], "password")' $password)
echo "$pass"
# Step 2 – Shell script to add a user and password on Linux
#!/bin/bash
# Purpose - Script to add a user to Linux system including passsword
# Author - Vivek Gite <www.cyberciti.biz> under GPL v2.0+
# ------------------------------------------------------------------
# Am i Root user?
if [ $(id -u) -eq 0 ]; then
	read -p "Enter username : " username
	read -s -p "Enter password : " password
	egrep "^$username" /etc/passwd >/dev/null
	if [ $? -eq 0 ]; then
		echo "$username exists!"
		exit 1
	else
		pass=$(perl -e 'print crypt($ARGV[0], "password")' $password)
		useradd -m -p "$pass" "$username"
		[ $? -eq 0 ] && echo "User has been added to system!" || echo "Failed to add a user!"
	fi
else
	echo "Only root may add a user to the system."
	exit 2
fi
# Step 3 – Change existing Linux user’s password in one CLI
echo "vivek:password" | chpasswd

# Verify that password has been changed
chage -l vivek
# Step 4 – Create Users and change passwords with passwd on a CentOS/RHEL
echo "YourPassword" | passwd --stdin UserName
系統帳號與密碼遷移

在來源主機執行

# 範例一: 遷移 uid=500 以上的所有帳號
ID_minimum=500
for f in /etc/{passwd,group}; do awk -F: -vID=$ID_minimum '$3>=ID && $1!="nfsnobody"' $f |sort -nt: -k3 > ${f#/etc/}.bak; done
while read line; do grep -w "^${line%%:*}" /etc/shadow; done <passwd.bak >shadow.bak
while read line; do grep -w "^${line%%:*}" /etc/gshadow; done <group.bak >gshadow.bak

# 範例二: 遷移 uid=501 以上的所有帳號
export UGIDLIMIT=501
awk -v LIMIT=$UGIDLIMIT -F: '($3>=LIMIT) && ($3!=65534)' /etc/passwd | sed '/nfsnobody/d' > passwd.move
awk -v LIMIT=$UGIDLIMIT -F: '($3>=LIMIT) && ($3!=65534)' /etc/group | sed '/nfsnobody/d' > group.move
awk -v LIMIT=$UGIDLIMIT -F: '($3>=LIMIT) && ($3!=65534) {print $1}' /etc/passwd | egrep -wf - /etc/shadow | sed '/nfsnobody/d' > shadow.move

# 範例三: 遷移 uid=501 ~ 600 的帳號
export UGID_DOWN=501
export UGID_UP=600
awk -v LIMIT_DOWN=$UGID_DOWN -v LIMIT_UP=$UGID_UP -F: '($3>=LIMIT_DOWN) && ($3<=LIMIT_UP) && ($3!=65534)' /etc/passwd | sed '/nfsnobody/d' > passwd.move
awk -v LIMIT_DOWN=$UGID_DOWN -v LIMIT_UP=$UGID_UP -F: '($3>=LIMIT_DOWN) && ($3<=LIMIT_UP) && ($3!=65534)' /etc/group | sed '/nfsnobody/d' > group.move
awk -v LIMIT_DOWN=$UGID_DOWN -v LIMIT_UP=$UGID_UP -F: '($3>=LIMIT_DOWN) && ($3<=LIMIT_UP) && ($3!=65534) {print $1}' /etc/passwd | egrep -wf - /etc/shadow | sed '/nfsnobody/d' > shadow.move

# 範例四: uid= 501 ~ 699 and 1000+
export UGIDLIMIT_LOW=501
export UGIDLIMIT_HIGH=699
export UGIDS_RHEL7=1000

awk -v RHEL7=$UGIDS_RHEL7 -v LIMIT_LOW=$UGIDLIMIT_LOW -v LIMIT_HIGH=$UGIDLIMIT_HIGH -F: '($3>=RHEL7) || (($3>=LIMIT_LOW) && ($3<=LIMIT_HIGH) && ($3!=65534))' /etc/passwd | sed '/nfsnobody/d' > passwd.move

awk -v RHEL7=$UGIDS_RHEL7 -v LIMIT_LOW=$UGIDLIMIT_LOW -v LIMIT_HIGH=$UGIDLIMIT_HIGH -F: '($3>=RHEL7) || (($3>=LIMIT_LOW) && ($3<=LIMIT_HIGH) && ($3!=65534))' /etc/group | sed '/nfsnobody/d' > group.move

awk -v RHEL7=$UGIDS_RHEL7 -v LIMIT_LOW=$UGIDLIMIT_LOW -v LIMIT_HIGH=$UGIDLIMIT_HIGH -F: '($3>=RHEL7) || (($3>=LIMIT_LOW) && ($3<=LIMIT_HIGH) && ($3!=65534)) {print $1}' /etc/passwd | egrep -f - /etc/shadow | sed '/nfsnobody/d' > shadow.move
NOTE: 如果系統有設定群組密碼，還要加上檔案 /etc/gshadow 的遷移。

將以上的檔案 *.move 複製到目的主機，然後執行

cat passwd.move >> /etc/passwd
cat shadow.move >> /etc/shadow
cat group.move >> /etc/group

pwconv
grpconv

# 帳號如果需要建立 home 目錄，可以執行
mkhomedir_helper <user-name>

Optional: 清除之前匯入的帳密

NOTE: 清除帳密時，只需要編輯 /etc/passwd 與 /etc/group，然後執行 pwconv 與 grpconv，就可以自動更新 /etc/shadow 與 /etc/gshadow。這方法不適用在匯入帳密時。
# 清除之前匯入的帳密
## 修改 /etc/passwd
vipw

## 修改 /etc/group
vigr

## 更新 /etc/shadow, /etc/gshadow
pwconv
grpconv

Optional: 批次建立 Home 目錄

for uidgid in $(cut -d: -f3,4 passwd.move); do
    dir=$(awk -F: /$uidgid/{print\$6} passwd.move)
    mkdir -vm700 "$dir"; cp -r /etc/skel/.[[:alpha:]]* "$dir"
    chown -R $uidgid "$dir"; ls -ld "$dir"
done
帳號活動監控 psacct
yum install psacct
遠端連線自動登出 (TMOUT)

Linux: /etc/profile.d/timeout.sh

#!/bin/bash
# Set the TMOUT 600 for specified group
grpname="sshusers"
#if [[ "`id -Gn`" =~ .*"$grpname".* ]]; then
if grep -q "$grpname" <<< "`id -Gn`"; then
    export TMOUT=600
fi

Multi groups

#!/bin/bash
# Set the TMOUT 600 for specified groups
#grpnames="(group1|group2|group3)"
grpnames="(sshusers)"
if echo "`id -Gn`" | grep -wEq "$grpnames"; then
    export TMOUT=600
fi

AIX: /etc/profile

# Set the TMOUT 600 for specified groups
#grpnames="(group1|group2|group3)"
grpnames="(sshusers)"
if echo "`id -Gn`" | grep -wEq "$grpnames"; then
    export TMOUT=600
fi

Learning


Windows AD 認證

登入 RedHat 系統時，可使用 Windows AD 帳號。

RedHat 7/8 (不加入網域)

這個方式需要先建立相同名稱的本機帳號，通常這個會違反資安規範。

安裝需要的套件

yum install sssd sssd-tools krb5-workstation krb5-libs

新增本地帳號與 AD 帳號同名

useradd AD_user

編輯 /etc/nsswitch.conf

# Add 'sss' for AD authentication
passwd:     files sss systemd
shadow:     files sss
group:      files sss systemd

編輯 /etc/krb5.conf

[logging]
 default = FILE:/var/log/krb5libs.log
 kdc = FILE:/var/log/krb5kdc.log
 admin_server = FILE:/var/log/kadmind.log

[libdefaults]
 dns_lookup_realm = false
 ticket_lifetime = 24h
 renew_lifetime = 7d
 forwardable = true
 rdns = false
 pkinit_anchors = FILE:/etc/pki/tls/certs/ca-bundle.crt
# Change this as required
 default_realm = EXAMPLE.COM
 default_ccache_name = KEYRING:persistent:%{uid}

[realms]
# Change this as required
EXAMPLE.COM = {
    kdc = ad.example.com
    dmin_server = ad.example.com
}

[domain_realm]
# Change this as required
.example.com = EXAMPLE.COM
example.com = EXAMPLE.COM

新增 /etc/sssd/sssd.conf

[sssd]
    services = nss, pam
    domains = EXAMPLE.COM

[domain/EXAMPLE.COM]
    id_provider = files
    auth_provider = krb5
    krb5_realm = EXAMPLE.COM
    krb5_server = ad.example.com

設定檔權限

chmod 0600 /etc/sssd/sssd.conf

啟動 sssd 服務

systemctl start sssd
systemctl enable sssd

編輯 /etc/pam.d/system-auth

#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      pam_env.so
auth        required      pam_faildelay.so delay=2000000
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 1000 quiet_success
# AD Authentication
auth        sufficient    pam_sss.so forward_pass

auth        required      pam_deny.so


account     required      pam_unix.so
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 1000 quiet
# AD Authentication
account     [default=bad success=ok user_unknown=ignore] pam_sss.so

account     required      pam_permit.so


password    requisite     pam_pwquality.so try_first_pass local_users_only retry=3 authtok_type$
password    sufficient    pam_unix.so sha512 shadow nullok try_first_pass use_authtok
# AD Authentication
password    sufficient    pam_sss.so use_authtok

password    required      pam_deny.so


session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
-session     optional      pam_systemd.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so
# AD Authentication
session     optional      pam_sss.so

編輯 /etc/pam.d/password-auth ，內容與上述的一樣。

驗證AD登入

本機驗證

#> kinit AD_user
Password for AD_user@EXAMPLE.COM:

#> klist
Ticket cache: KEYRING:persistent:0:0
Default principal: AD_user@EXAMPLE.COM

Valid starting     Expires            Service principal
11/02/20 04:16:38  11/02/20 14:16:38  krbtgt/EXAMPLE.COM@EXAMPLE.COM
	renew until 18/02/20 04:16:34

遠端 SSH 驗證

遠端使用 AD_user ( 不需加 @example.com )登入 SSH。

其他指令

Displaying user authorization details

sssctl user-checks -a acct -s sshd AD_user

Display a list of available domains

sssctl domain-list

RedHat 7/8 (加入網域)

安裝需要套件

yum install sssd realmd oddjob oddjob-mkhomedir adcli \
  samba-common samba-common-tools krb5-workstation \
  openldap-clients policycoreutils-python

使用 realmd 將 Linux 主機加入 AD 網域

NOTE: 建議先將 /etc/krb5.conf 恢復成初始值，如果曾經修改過。還有將 /etc/sssd/sssd.conf 移除。

加入 AD 網域時，需要有 AD 管理員或有足夠權限的 AD 帳號 例如 adm1。

一旦加入網域成功，系統會自動修改或建立這兩個檔案。

realm discover ad.example.com

realm join ad.example.com -U adm1

realm list

自動生成 /etc/sssd/sssd.conf, /etc/krb5.conf 

[sssd]
domains = example.com
config_file_version = 2
services = nss, pam

[domain/example.com]
ad_server = ad.example.com
ad_domain = example.com
krb5_realm = EXAMPLE.COM
realmd_tags = manages-system joined-with-adcli
cache_credentials = True
id_provider = ad
krb5_store_password_if_offline = True
default_shell = /bin/bash
ldap_id_mapping = True
use_fully_qualified_names = True
fallback_homedir = /home/%u@%d
access_provider = ad
[libdefaults]
 dns_lookup_realm = false
 ticket_lifetime = 24h
 renew_lifetime = 7d
 forwardable = true
 rdns = false
 pkinit_anchors = FILE:/etc/pki/tls/certs/ca-bundle.crt
 default_ccache_name = KEYRING:persistent:%{uid}

 default_realm = EXAMPLE.COM
[realms]
 EXAMPLE.COM = {
 }

[domain_realm]
 example.com = EXAMPLE.COM
 .example.com = EXAMPLE.COM

Optional: 主機退出 AD 網域

# 預設需要 AD 的 Administrator 密碼
realm leave ad.example.com

# 或者使用指定的帳密
realm leave ad.example.com -U 'EXAMPLE.COM\user'

登入存取控制

預設，網域所有帳號都可以登入主機；要限制可以存取主機的 AD 帳號或 AD 群組，需要修改 /etc/sssd/sssd.conf。

編輯 /etc/sssd/sssd.conf

# ACL for AD Login
#access_provider = ad
access_provider = simple
#simple_allow_users = ad-user1, ad-user2
simple_allow_groups = ad-group

重啟 sssd 服務

systemctl restart sssd
realm list
帳號管理

加入 ad-user 至本機群組

usermod -aG local-group aduser@ad.domain.com
getent group local-group
groups aduser@ad.domain.com

更多指令

列出 AD 帳號的 uid

id ADDOMAIN\\aduser@ad.domain.com

getent passwd aduser@ad.domain.com