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How do groups work on Linux?

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Re: How do groups work on Linux?

#11

Post by dozzie »

delinka wrote: post #8
dozzie wrote: post #6

Earlier quoted context omitted.

[dozzie@zorn /srv]$ ls -ld foo drwxrwxrwx 2 root wheel uarch 2 Nov 21 12:57 foo/ [dozzie@zorn /srv]$ touch foo/nabla [dozzie@zorn /srv]$ ls -l foo/nabla -rw-r--r-- 1 dozzie wheel uarch 0 Nov 21 12:58 foo/nabla [dozzie@zorn /srv]$ id uid=1001(dozzie) gid=1001(dozzie) groups=1001(dozzie) [dozzie@zorn /srv]$ uname -s -r FreeBSD 11.0-RELEASE-p1 This is called "BSD semantics". You can get the same behaviour with appropria…

While it’s nice to have it as default behavior when it makes sense, it’s also nice to have setgid as an option rather than the rule.

Nice or not, you can't talk about directory's SGID behaviour as it was unversal truth, because it's Linux-specific, and even then it's something that can be changed.

Re: How do groups work on Linux?

#12

Post by Asooka »

Ohh, so THAT's why I have to log out and back in to have my group changes take effect. That, along with having to start a new shell to pick up new env vars from ~/.profile, are my two biggest annoyances with the Linux process model. Reminds me a bit of the Windows 98 days when you had to restart to change your IP address. I really wish someone would sit down and figure out how to propagate group and environment changes to already running processes and implement them.

Re: How do groups work on Linux?

#13

Post by heywire »

Asooka wrote: post #12

Ohh, so THAT's why I have to log out and back in to have my group changes take effect. That, along with having to start a new shell to pick up new env vars from ~/.profile, are my two biggest annoyances with the Linux process model. Reminds me a bit of the Windows 98 days when you had to restart to change your IP address. I really wish someone would sit down and figure out how to propagate group and environment chang…

Take a look at the command “newgrp”

Re: How do groups work on Linux?

#14

Post by laumars »

dozzie wrote: post #10
jwilk wrote: post #7

Earlier quoted context omitted.

What filesystem was that? And why is this behavior filesystem-specific?

Not what filesystem , it's what OS . FreeBSD. And ZFS, but UFS works the same.

I could be wrong but I thought the file system's "drivers" did the handling of file system permissions rather than the OS / kernel? Or at least this was my experience when playing around with FUSE on hobby projects.

Re: How do groups work on Linux?

#15

Post by bartbes »

Asooka wrote: post #12

Ohh, so THAT's why I have to log out and back in to have my group changes take effect. That, along with having to start a new shell to pick up new env vars from ~/.profile, are my two biggest annoyances with the Linux process model. Reminds me a bit of the Windows 98 days when you had to restart to change your IP address. I really wish someone would sit down and figure out how to propagate group and environment chang…

You can load your .profile into your current shell using either '. ~/.profile' or 'source ~/.profile'.

Re: How do groups work on Linux?

#17

Post by rubbsdecvik »

chairmanwow wrote: post #3

I absolutely love Julia Evan's writing. I find her articles / zines to cover interesting and useful technical topics while remaining _extremely_ accessible to me (especially when I was a student)! I really admire her ability to present technical topics in plain language.

I fully agree. Even on topics I feel I know well, she's 1) shown me something I didn't know, and 2) shown me how a "newbie" could see the topic, making it easier for me to help teach/mentor someone else.

Re: How do groups work on Linux?

#18

Post by laumars »

dozzie wrote: post #11
delinka wrote: post #8

Earlier quoted context omitted.

While it’s nice to have it as default behavior when it makes sense, it’s also nice to have setgid as an option rather than the rule.

Nice or not, you can't talk about directory's SGID behaviour as it was unversal truth, because it's Linux-specific, and even then it's something that can be changed.

Except it does work FreeBSD:

    [lau@primus ~/test]$ mkdir setgid nosetgid
    
    [root@primus /home/lau/test]# chmod g+s setgid
    
    [root@primus /home/lau/test]# chgrp lau setgid
    
    [lau@primus ~/test]$ ls -l
    total 1
    drwxr-xr-x  2 lau  users  4 21 Nov 14:52 nosetgid
    drwxr-sr-x  2 lau  lau    4 21 Nov 14:51 setgid
    
    [lau@primus ~/test]$ touch {nosetgid,setgid}/test
    
    [lau@primus ~/test]$ ls -l *
    nosetgid:
    total 1
    -rw-r--r--  1 lau   users  0 21 Nov 14:52 test
    
    setgid:
    total 1
    -rw-r--r--  1 lau   lau    0 21 Nov 14:51 test
Looking at your example, I'd guess you didn't set the setgid bit as your `ls` doesn't show the group column to be `S` (instead stating `X` which is the default a directory would be set as).

OS build and file system:

    [lau@primus ~/test]$ uname -a
    FreeBSD primus 10.3-RELEASE-p11 FreeBSD 10.3-RELEASE-p11 #0: Mon Oct 24 18:49:24 UTC 2016     root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
    
    [lau@primus ~/test]$ mount | grep " / "
    zroot2 on / (zfs, local, nfsv4acls)

Re: How do groups work on Linux?

#19

Post by dozzie »

laumars wrote: post #18
dozzie wrote: post #11

Earlier quoted context omitted.

Nice or not, you can't talk about directory's SGID behaviour as it was unversal truth, because it's Linux-specific, and even then it's something that can be changed.

Except it does work FreeBSD: [lau@primus ~/test]$ mkdir setgid nosetgid [root@primus /home/lau/test]# chmod g+s setgid [root@primus /home/lau/test]# chgrp lau setgid [lau@primus ~/test]$ ls -l total 1 drwxr-xr-x 2 lau users 4 21 Nov 14:52 nosetgid drwxr-sr-x 2 lau lau 4 21 Nov 14:51 setgid [lau@primus ~/test]$ touch {nosetgid,setgid}/test [lau@primus ~/test]$ ls -l * nosetgid: total 1 -rw-r--r-- 1 lau users 0 21 Nov…

> Except it does work FreeBSD:

Congratulations, you have an incomplete example.

And what exactly did you want to prove? That an OS-specific behaviour can be exhibited by more than one OS?

Re: How do groups work on Linux?

#20

Post by mason55 »

The book she mentions, "The Linux Programming Interface," sounds pretty useful, but it's seven years old at this point. Does anyone know how much has changed or if there's a new version coming any time soon? Seems like it's worth $70 but the age has me concerned. I'm sure the basics, like the things this article is about, haven't changed, but I bet all the stuff around cgroups would be useful for how setgid works with a process.
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