...

Hi,

we are upgrading some servers from C6 to C7 with a lot of user accounts on them (UID>=500). CentOS 7 has MIN_UID/MIN_GID 1000, Centos 6 has 500 in login.defs.

Can I change in /etc/login.defs MIN_UID/MIN_GID to 500 for C7? So I could just grep the users out from passwd/shadow/group files and append them to the Centos7 passwd/shadow/group files. Can this do any damage to CentOS7 later on? Thinking about updates....

When I did an upgrade from CentOS 5 to 7 I found that even a standard install of CentOS 7 already used a number of GIDs in the range of 500-999.

In the end I decided to rearrange all users to new UIDs/GIDs and converted all storage with a script.

The tricky part was to find a way which doesn't take ages to convert storage. Doing so with find.... wasn't possible for performance reasons.

Attached script was used to convert every user. It was the fastest way I found. The script was started in background for every user.

Looks like attachments are stripped from the mail, so here is the script embedded:

----%<---- #!/bin/bash

if (( $# < 3 )); then echo "Usage: $0 <username> <new uid> <dir> [<dir>...]" echo "Example: $0 user1 1000 /tmp /etc /usr /opt /var /home" exit 1 fi

USR=$1 NEW_UID=$2 NEW_GID=

shift 2 DIRS=$@

OLD_UID=$(id -u $USR) OLD_GID=$(id -g $USR)

if [[ -z "$NEW_GID" ]]; then NEW_GID=$NEW_UID fi

echo "modifying user $USR ids ${OLD_UID}:${OLD_GID} -> ${NEW_UID}:${NEW_GID} on $DIRS"

# Note: usermod changes ownership of at least $HOME and /var/spool/mail/${USR} groupmod -g $NEW_GID $USR usermod -u $NEW_UID -g $USR $USR

chown --changes --silent --no-dereference --preserve-root --recursive --from=:${OLD_GID} :${NEW_GID} $DIRS chown --changes --silent --no-dereference --preserve-root --recursive --from=${OLD_UID} ${NEW_UID} $DIRS ----%<----

On 10/22/20 3:21 PM, Louis Lagendijk wrote:

On Thu, 2020-10-22 at 15:13 +0200, Thomas Plant wrote:

...

Am 22.10.2020 um 14:11 schrieb Thomas Plant:

...

Hi,

we are upgrading some servers from C6 to C7 with a lot of user accounts on them (UID>=500). CentOS 7 has MIN_UID/MIN_GID 1000, Centos 6 has 500 in login.defs.

Can I change in /etc/login.defs MIN_UID/MIN_GID to 500 for C7? So I could just grep the users out from passwd/shadow/group files and append them to the Centos7 passwd/shadow/group files. Can this do any damage to CentOS7 later on? Thinking about updates....

Thanks, Thomas _______________________________________________ CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos

Thanks, for the hints.

Think I will go the lazy way and adapt login.defs. ;-)

Greetings, Thomas _______________________________________________ CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos

You better don't do that: when I looked at one of my C8 boxes there were many services that require a system account (but not a global fixed one) were allocated from the top of the 500-999 range. Bite the bullet and change user accounts. to start from 1000. Especially when using NFS this may otherwise come back and bite you

I've been though the need of similar changes at least twice. Fist time when I was migrating servers from SunOS, where reserves UIG/GID number were 0-100, to RedHat (and CentOS) Linuxes (0-500), and the second time when Linux went up to 0-1000. In both cases the analyses what would be right thing was short, and the transition was just to find how far up to move UIDs/GIDs of existing users in the range 101-500 or 501-1000. The rest of the users stayed the same. Otherwise you may get an "unusual" for its breed system with lot of surprises in a future, especially if some new sysadmin comes to take care if the machine.

Just my $0.02.

Valeri

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