Introduction
Migrating users from one Linux system to another can be a complex task, but with the right steps and careful planning, it can be accomplished smoothly. In this guide, we will walk you through the process of migrating users, their passwords, groups, and home folders from one Linux system to another. We’ll be using bash scripts to automate the backup and restore process, ensuring a seamless transition.
The following items will not be covered by our instructions:
- User limits
- Group password
Step 1: Backup User Information on the Source Server
First, log in to the source Linux system and open a terminal. Use the following command to get a list of all users:
lslogins -o "USER,UID,GECOS,HOMEDIR,SHELL,GROUP,GID,SUPP-GROUPS,SUPP-GIDS"
Next, identify the users you want to migrate and add their names to the users_to_backup variable in the provided script:
backup_password_file="etc-passwd-bak"
backup_group_file="etc-group-bak"
backup_shadow_file="etc-shadow-bak"
# Add more users separated by spaces if needed
users_to_backup="linus lennart"
for user in $users_to_backup ; do
curuser=$user
echo -e "\n=> User is $curuser"
curid=$(id -u "$curuser")
curgid=$(id -g "$curuser")
cursupgit=$(id -G "$curuser")
echo "User id is $curid"
echo "User group id is $curgid"
echo "User supplementary groups are $cursupgit"
echo "Backing up /etc/passwd for $curuser"
grep -E "^${curuser}:.:${curid}" /etc/passwd >> "$backup_password_file"
echo "Backing up primary group for $curuser"
if [ -f "$backup_group_file" ] ; then
if grep -q ":${curid}:" "$backup_group_file" ; then
echo "Group already backed up"
else
grep ":${curid}:" /etc/group >> "$backup_group_file"
fi
else
grep ":${curid}:" /etc/group >> "$backup_group_file"
fi
echo "Backing up secondary groups for $curuser"
for groupid in $cursupgit ; do
if grep -q ":${groupid}:" "$backup_group_file" ; then
echo "Group already backed up"
else
grep ":${groupid}:" /etc/group >> "$backup_group_file"
fi
done
echo "Backing up /etc/shadow for $curuser"
sudo grep -E "^$curuser" /etc/shadow >> "$backup_shadow_file"
done
Save the script to a file, e.g., user_backup_script.sh, and make it executable:
chmod +x user_backup_script.sh
Execute the script as root:
sudo ./user_backup_script.sh
The script will back up user information, including passwords and group data, to the specified backup files.
Step 2: Copy Backup Files to the Destination Server
Next, copy the three backup files (etc-passwd-bak, etc-group-bak, and etc-shadow-bak) from the source server to the destination server using the scp command or any preferred method.
# Example using scp
scp etc-*-bak user@destination_server:/path/to/backup_files/
Step 3: Restore Users on the Destination Server
Log in to the destination Linux system and open a terminal. Navigate to the directory where the backup files are located and run the provided restore script as root:
backup_password_file="etc-passwd-bak"
backup_group_file="etc-group-bak"
backup_shadow_file="etc-shadow-bak"
echo -e "\n=> Backing up the system files"
for file in /etc/{passwd,group,shadow} ; do
cp -v "$file" "${file}_$(date -I)"
done
echo -e "\n=> Restoring users"
cat "$backup_password_file" | while read -r line ; do
userid="$(echo "$line" | awk -F":" '{print $3}')"
username="$(echo "$line" | awk -F":" '{print $1}')"
echo "-> Restoring user $username"
if grep -Eq "^${username}:.:${userid}" /etc/passwd ; then
echo " ERROR: User ID already exists. Manual intervention is needed"
else
echo "$line" >> /etc/passwd
if grep -qE "^${username}:" /etc/shadow ; then
echo " ERROR: User password already exists. Manual intervention is needed"
else
grep -E "^${username}:" "$backup_shadow_file" >> /etc/shadow
fi
fi
done
echo -e "\n=> Restoring groups"
cat "$backup_group_file" | while read -r line ; do
groupid="$(echo "$line" | awk -F":" '{print $3}')"
groupname="$(echo "$line" | awk -F":" '{print $1}')"
echo "-> Restoring group $groupname"
if grep -qE "^${groupname}:.:${groupid}" /etc/group ; then
echo " ERROR: Group already exists. Manual intervention may be needed"
else
echo "$line" >> /etc/group
fi
done
Run the restore script:
sudo ./user_restore_script.sh
The script will restore the users and their passwords, taking care to avoid conflicts with existing user IDs. Pay close attention to error messages and take action if needed. If there are any error messages related to system group creation, it might be acceptable as the groups may already exist on the new system.
Step 4: Copy Home Folders and Set Permissions
Finally, to complete the migration, copy the home folders for the desired users from the source server to the destination server using rsync:
# Replace 'user1,user2,user3' with appropriate values
# Replace 'destination_server' with appropriate values
rsync -avzh -e ssh /home/{user1,user2,user3} user@destination_server:/home/
Ensure that the permissions and ownership are set correctly for the home folder of each user on the destination server:
# Replace user and primary_group with appropriate values
sudo chown -R user:primary_group /home/user
Note: For SFTP users that use CHROOT, the user’s home folder needs to be owned by ‘root’
Conclusion:
Migrating users from one Linux system to another involves a series of crucial steps, including backup, restoration, and copying of home folders. By using the provided scripts and following this step-by-step guide, you can ensure a smooth and successful user migration process. Always exercise caution during the migration and verify the results to ensure everything is functioning as expected on the destination system.
Additional reading:
