[CentOS] nsswitch.conf, ldap, local groups problem

Mark Hennessy mark at hennessy.cx
Wed Aug 27 21:56:28 UTC 2008


Quoting Craig White <craigwhite at azapple.com>:

> On Wed, 2008-08-27 at 17:35 -0400, Mark Hennessy wrote:
>> Quoting Craig White <craigwhite at azapple.com>:
>>
>> > On Wed, 2008-08-27 at 17:07 -0400, Mark Hennessy wrote:
>> >> Quoting Craig White <craigwhite at azapple.com>:
>> >>
>> >> > On Wed, 2008-08-27 at 14:53 -0400, Mark Hennessy wrote:
>> >> >> Quoting Craig White <craigwhite at azapple.com>:
>> >> >>
>> >> >> > On Wed, 2008-08-27 at 12:34 -0400, Mark Hennessy wrote:
>> >> >> >> I'm using CentOS 5.0,5.1, and 5.2 on several systems where  
>>  I'm seeing
>> >> >> >> this problem.
>> >> >> >>
>> >> >> >> Hello, I'm seeing a weird problem that perhaps someone has run into
>> >> >> >> with groups.
>> >> >> >>
>> >> >> >> First, a little background.
>> >> >> >> I was made aware of a problem with CentOS 5 where if the   
>> nscd password
>> >> >> >> cache is clear and
>> >> >> >> someone tries to log in if there is no network connection   
>> with an LDAP
>> >> >> >> account that it
>> >> >> >> just hangs.  Even worse, if the machine is rebooted and it  
>>  continues
>> >> >> >> to have no network
>> >> >> >> connection, even root login doesn't work.  I messed around with
>> >> >> >> nsswitch.conf to fix this
>> >> >> >> problem.
>> >> >> >>
>> >> >> >> I altered these lines as so:
>> >> >> >> passwd:     files [!NOTFOUND=return] ldap
>> >> >> >> shadow:     files [!NOTFOUND=return] ldap
>> >> >> >> group:      files [!NOTFOUND=return] ldap
>> >> >> >>
>> >> >> >> and the problem seemed to go away.
>> >> >> >>
>> >> >> >> But now, here's the weird stuff:
>> >> >> >> I have defined in my local /etc/groups file this line:
>> >> >> >> group1:x:100:apache
>> >> >> >> group2:x:101:apache
>> >> >> >>
>> >> >> >> 'getent group groupname' shows the right info:
>> >> >> >> # getent group group1
>> >> >> >> group1:x:100:apache
>> >> >> >>
>> >> >> >> # sudo -u apache bash
>> >> >> >> $ groups
>> >> >> >> apache
>> >> >> >>
>> >> >> >> I revert back to my old config:
>> >> >> >> # sudo -u apache bash
>> >> >> >> $ groups
>> >> >> >> apache group1 group2
>> >> >> >>
>> >> >> >> Also, something else that's interesting. If I do this:
>> >> >> >> passwd:     files [!NOTFOUND=return] ldap
>> >> >> >> shadow:     files [!NOTFOUND=return] ldap
>> >> >> >> group:      ldap [NOTFOUND=continue] files
>> >> >> >>
>> >> >> >> and reboot, udev segfaults and the system freezes up after a few
>> >> >> >> more seconds.
>> >> >> >> Starting udev: /sbin/start_udev: line 43:   519 Segmentation fault
>> >> >> >>   "$@" $ARGS
>> >> >> >> /sbin/start_udev: line 201:   523 Segmentation fault
>> >> /sbin/udevd -d
>> >> >> >> Wait timeout. Will continue in the background.[FAILED]
>> >> >> >>
>> >> >> >> Any advice?
>> >> >> > ----
>> >> >> > Try putting this at the bottom of /etc/ldap.conf
>> >> >> >
>> >> >> > timelimit 30
>> >> >> > bind_timelimit 30
>> >> >> > bind_policy soft
>> >> >> > nss_initgroups_ignoreusers root,ldap
>> >> >> >
>> >> >> > I wouldn't recommend the changes that you have in nsswitch.conf
>> >> >>
>> >> >> Unfortunately, that doesn't work either.
>> >> >> I made the changes, shut down the machine and started it without
>> >> >> networking, and here's what happens:
>> >> >>
>> >> >> login: root
>> >> >> Password:
>> >> >>
>> >> >> login:
>> >> >>
>> >> >> login pukes and init starts it again.
>> >> > ----
>> >> > you shouldn't need to restart but if you can't login as root, you
>> >> > probably still have something messed up in /etc/nsswitch.conf or may
>> >> > have messed up /etc/passwd | /etc/shadow
>> >> >
>> >> > can you login as a user and su - to root?
>> >> >
>> >> > if not, it probably would be best to boot to runlevel 1 and
>> >> > edit /etc/nsswitch.conf so it has this...
>> >> >
>> >> > passwd:     files ldap
>> >> > shadow:     files ldap
>> >> > group:      files ldap
>> >> >
>> >> > and remove the NOTFOUND entries
>> >>
>> >> Yes, done.
>> >> Without networking, still the login failure trouble.
>> >>
>> >> With networking, no trouble at all, but with those timeouts of 30
>> >> seconds and without those changes to nsswitch.conf, it takes a while
>> >> for the first root login to succeed even though it is using local auth.
>> > ----
>> > do you have this line in /etc/pam.d/system-auth
>> >
>> > account     sufficient    pam_localuser.so
>> >
>> > ???
>> >
>> > What does your /etc/pam.d/system-auth look like?
>> my /etc/pam.d/system-auth:
>> #%PAM-1.0
>> # This file is auto-generated.
>> # User changes will be destroyed the next time authconfig is run.
>> auth        required      pam_env.so
>> auth        sufficient    pam_unix.so nullok try_first_pass
>> auth        requisite     pam_succeed_if.so uid >= 500 quiet
>> auth        sufficient    pam_ldap.so use_first_pass debug
>> auth        required      pam_deny.so
>>
>> account     required      pam_unix.so broken_shadow
>> account     sufficient    pam_succeed_if.so uid < 500 quiet
>> account     [default=bad success=ok user_unknown=ignore] pam_ldap.so
>> account     required      pam_permit.so
>>
>> password    requisite     pam_cracklib.so try_first_pass retry=3
>> password    sufficient    pam_unix.so md5 shadow nullok try_first_pass
>> use_authtok
>> password    sufficient    pam_ldap.so use_authtok debug
>> password    required      pam_deny.so
>>
>> session     optional      pam_keyinit.so revoke
>> session     required      pam_limits.so
>> session     [success=1 default=ignore] pam_succeed_if.so service in
>> crond quiet use_uid
>> session     required      pam_unix.so
>> session     optional      pam_ldap.so debug
>> session     required      pam_mkhomedir.so skel=/etc/skel umask=0022
>>
>>
>> ===
>> I added
>>
>> account     sufficient    pam_localuser.so
>>
>> right before pam_ldap in the account section and tried again with the
>> same procedure (turn off networking (chkconfig --levels 2345 network
>> off), reboot).
>>
>> Same result, login dies and gets restarted.
>>
>> login: root
>> Password:
>>
>> login:
> ----
> well, it hardly makes any sense to use ldap for user accounts and start
> up with networking off but I would recommend that you adhere to the
> advice at the top of the file and run 'authconfig' or
> 'system-config-authentication', make sure the settings are correct
> (including checking the box for local authentication is sufficient) so
> that it configures not only /etc/pam.d/system-auth and nsswitch.conf

Yes, I agree, it makes no sense to operate a machine with ldap  
accounts if it has no network connection, but at least one should be  
able to log in as root.  To clarify, here's the problem:
I have a machine.  In normal operation, the network connection is  
non-functional and LDAP accounts are usable and everyone does their  
thing over ssh.  If the network connection craps out, I can get into  
the machine via serial console and try to find out what's going on,  
perhaps switch to a different network connection, whatever.  If I  
can't log in as root, my only recourse is to powercycle the machine  
and go into single-user mode.  Now, multiply that by 100.  This is why  
I need to get this working.

> Craig
>





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