In order to successfully implement w/r access via ACL for external storage with ext4 fs I need to assign default group id for files on storage.

LSB_5.0.0 say:

This specification makes no attempt to numerically assign user or group identity numbers, with the exception that both the User ID and Group ID for the user root shall be equal to 0. 

Shame for Linux vendors!

Are there any convention about group ids among major Linux distros?

In Debian policy I found that default group values defined by base-passwd package in /usr/share/base-passwd/group.master file. Among them this groups look good candidate for ACL defaults:

tape:*:26: backup:*:34: operator:*:37: plugdev:*:46: staff:*:50: users:*:100: nogroup:*:65534: 

Never works with Suse/RH/Slackware distros policy documents... Also interesting if FreeBSD/OpenBSD/MacOS share convention with Linux distros.

UPDATE I compare MacOS X (dscacheutil -q group) with Debian and only few group ids are matched:

sys:*:3: 

UPDATE 2 I compare FreeBSD and Debian /etc/group file, only 2 matches:

daemon:*:1: sys:*:3: