Copy Users, Groups and Passwords

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How to copy Users / Groups / Passwords from one Linux sysetm to another

You can migrate users from old Linux server to new Linux sever with standard commands such as tar, awk, scp and others. This is also useful if you are using old Linux distribution such as Redhat 9 or Debian 2.x.

 Following files and /dirs are required for Linux user management:

1. /etc/passwd
2. /etc/shadow
3. /etc/group
4. /etc/gshadow - group shadow file (contains the encrypted password for group)
5. /var/spool/mail - Generally user emails are stored here.
6. /home

Commands to type on old Linux system

First create a tar ball of old uses (old Linux system). Create a directory:
# mkdir /root/move/
Setup UID filter limit:
# export UGIDLIMIT=500
Now copy /etc/passwd accounts to /root/move/passwd.mig using awk to filter out system account (i.e. only copy user accounts)
# awk -v LIMIT=$UGIDLIMIT -F: '($3>=LIMIT) && ($3!=65534)' /etc/passwd > /root/move/passwd.mig
Copy /etc/group file:
# awk -v LIMIT=$UGIDLIMIT -F: '($3>=LIMIT) && ($3!=65534)' /etc/group > /root/move/group.mig
Copy /etc/shadow file:
# awk -v LIMIT=$UGIDLIMIT -F: '($3>=LIMIT) && ($3!=65534) {print $1}' /etc/passwd | tee - |egrep -f - /etc/shadow > /root/move/shadow.mig
Copy /etc/gshadow (rarely used):
# cp /etc/gshadow /root/move/gshadow.mig
Make a backup of /home and /var/spool/mail dirs:
# tar -zcvpf /root/move/home.tar.gz /home
# tar -zcvpf /root/move/mail.tar.gz /var/spool/mail
Where,
  • Users that are added to the Linux system always start with UID and GID values of as specified by Linux distribution or set by admin. Limits according to different Linux distro:
    • RHEL/CentOS/Fedora Core : Default is 500 and upper limit is 65534 (/etc/libuser.conf).
    • Debian and Ubuntu Linux : Default is 1000 and upper limit is 29999 (/etc/adduser.conf).
  • You should never ever create any new system user accounts on the newly installed Cent OS Linux. So above awk command filter out UID according to Linux distro.
  • export UGIDLIMIT=500 - setup UID start limit for normal user account. Set this value as per your Linux distro.
  • awk -v LIMIT=$UGIDLIMIT -F: '($3>=LIMIT) && ($3!=65534)' /etc/passwd > /root/move/passwd.mig - You need to pass UGIDLIMIT variable to awk using -v option (it assigns value of shell variable UGIDLIMIT to awk program variable LIMIT). Option -F: sets the field separator to : . Finally awk read each line from /etc/passwd, filter out system accounts and generates new file /root/move/passwd.mig. Same logic is applies to rest of awk command.
  • tar -zcvpf /root/move/home.tar.gz /home - Make a backup of users /home dir
  • tar -zcvpf /root/move/mail.tar.gz /var/spool/mail - Make a backup of users mail dir


filter out system account (i.e. only copy user accounts) in file, before that please take the backup of above original files.

Use vi editor and paste the user account except system accounts.

1. tar -zcvpf /tmp/home.tar.gz /home - Make a backup of users /home dir
2. tar -zcvpf /tmp/mail.tar.gz /var/spool/mail - Make a backup of users mail dir

Do scp the files from one server to other:

scp -r /tmp/home.tar.gz user@<hostname>:/path/to/location
scp –r /tmp/mail.tar.gz user@<hostname>:/path/to/location

tar –xzvpf /tmp/home.tar.gz
tar -zxvpf /tmp/mail.tar.gz

reboot the server and login with your user ids.