This may be the same problem I reported in Bug #914674
I notice this behaviour as well:
[+16.19s] DEBUG: Dropping privileges to uid 6057
[+16.19s] DEBUG: Adding session authority to /npdisks/home/jb/.Xauthority
[+16.20s] DEBUG: Restoring privileges
[+16.20s] DEBUG: Launching process 7148: /usr/sbin/lightdm-session
'gnome-session --session=ubuntu'
[+16.20s] WARNING: Failed to change to home directory /npdisks/home/jb:
Permission denied
It looks like it restores privileges to root before trying to change to
home directory and this naturally fails since root has no privileges
there.
It looks like session.c tries to change working directory _before_ it
tries to change user:
session.c:
Line 409:
/* Change working directory */
if (chdir (user_get_home_directory (user)) != 0)
{
g_warning ("Failed to change to home directory %s: %s",
user_get_home_directory (user), strerror (errno));
_exit (EXIT_FAILURE);
}
/* Change to this user */
if (getuid () == 0)
{
if (initgroups (user_get_name (user), user_get_gid (user)) < 0)
{
g_warning ("Failed to initialize supplementary groups for %s: %s",
user_get_name (user), strerror (errno));
_exit (EXIT_FAILURE);
}
if (setgid (user_get_gid (user)) != 0)
{
g_warning ("Failed to set group ID to %d: %s", user_get_gid (user),
strerror (errno));
_exit (EXIT_FAILURE);
}
if (setuid (user_get_uid (user)) != 0)
{
g_warning ("Failed to set user ID to %d: %s", user_get_uid (user),
strerror (errno));
_exit (EXIT_FAILURE);
}
}
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https://bugs.launchpad.net/bugs/877766
Title:
lightdm login fails with NFS home and strict (mode 0700) permissions
Status in Light Display Manager:
Confirmed
Status in “lightdm” package in Ubuntu:
Triaged
Status in “lightdm” source package in Oneiric:
Triaged
Bug description:
Lightdm appears not to be able to log in a user if all of the
following are true:
1. They've got an NFS-mounted home directory
2. NFS is configured in the usual manner; ie, root privileges do not allow
access to arbitrary remote files
3. The user's home directory permissions are such that "other" cannot access
the directory (ie, mode 0700)
In this situation, the password is accepted and the screen clears.
Rather than bringing up the desktop as expected, a couple of seconds
pass and we're returned to the lightdm screen. This yielded a message
in one of the /var/log/lightdm logs which I've just discovered was
overwritten by subsequent successful logins. I'll recreate this and
update the bug tonight.
Workaround was to chmod the user's homedir to 0711 which allowed
lightdm to work properly.
Release is Ubuntu 11.10 with all updates as of 17 Oct 2011 at roughly
10pm EDT. Lightdm package is 1.0.1-0ubuntu6.
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https://bugs.launchpad.net/lightdm/+bug/877766/+subscriptions
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