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I've a group of users, all of which are in a single group. Then I have a Java daemon that is a member of a seperate group.

I want both the users and the daemon to have access to the same set of files. Apparently, adding the daemon to a secondary group so that this works is not generally workable.

What if I give the daemon ownership of files and directories and the group of all users group rights? What sort of problems might I see? Is this bad for security?

Do different UNIX and Linux environments interpret this differently? This environment is Linux: Ubuntu Lucid Lynx (10.04) Server.

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Seems that in such situations is much better to use acl. You need to install acl package and enable it in mount options. For example if /etc/fstab it looks like

/dev/mapper/server-home   /home    ext4    defaults,acl,noatime     0       2

You can manage right with setfacl command and check it with getfacl.

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How do I know if the filesystem supports ACLs? I realize that ext2, ext3, and ext4 have mount options acl and noacl; what is the default? (man pages don't specify) Likewise, are ACLs supported on filesystems like XFS? I think that XFS and many others (JFS, btrfs) will probably support ACLs completely; is this right? Can Java (yes, I know Java comes in many kinds!) handle ACLs or is it transparent? – Mei Dec 22 '11 at 19:02
Oh - and you didn't answer my question :) Aside from "doing the right thing" (using ACLs from the sound of it) I'd also like to know how these permissions resolve themselves and how UNIX/Linux handles it. – Mei Dec 22 '11 at 19:03

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