UNIX for Advanced & Expert Users

[root tmp]# groupadd test1
[root tmp]# groupadd test2
[root tmp]# useradd -g test1 a
[root tmp]# useradd -g test2 b
[root tmp]# passwd a
Changing password for user a.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[root tmp]# passwd b
Changing password for user b.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[root tmp]# su - a
[a ~]$ cd /tmp
[a tmp]$ id a
uid=517(a) gid=1039(test1) groups=1039(test1)
[a tmp]$ id b
uid=518(b) gid=1042(test2) groups=1042(test2)
[a tmp]$ mkdir debug
[a tmp]$ ls -tld debug/
drwxr-xr-x 2 a test1 4096 Aug 10 16:02 debug/
[a tmp]$ chmod 755 debug
[a tmp]$ ls -tld debug/
drwxr-xr-x 2 a test1 4096 Aug 10 16:02 debug/
[a tmp]$ id
uid=517(a) gid=1039(test1) groups=1039(test1)
[a tmp]$ setfacl -m  d:g:test2:rwx /tmp/debug
[a tmp]$ getfacl /tmp/debug
# file: tmp/debug
# owner: a
# group: test1
user::rwx
group::r-x
other::r-x
default:user::rwx
default:group::r-x
default:group:test2:rwx
default:mask::rwx
default:other::r-x

[a tmp]$ id
uid=517(a) gid=1039(test1) groups=1039(test1)
[a tmp]$ su - b
Password:
[b ~]$ cd /tmp/debug/
[b debug]$ touch 1
touch: cannot touch `1': Permission denied
[b debug]$ pwd
/tmp/debug
.

ls -lad /tmp

$ ls -lad /tmp
drwxrwxrwt 16 root root 4096 Aug 14 10:44 /tmp