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Running into an issue with openldap I've never had much success to tackle. We run openldap on another machine on its own vlan. Now if that ldap server dies anything that accesses uid or gid seems to be brought to a standstill till a timeout happens.

Here is my

/etc/nsswitch.conf

passwd:         compat [SUCCESS=return] ldap [unavail=return]
group:          compat [SUCCESS=return] ldap [unavail=return]
shadow:         compat [SUCCESS=return] ldap [unavail=return]



hosts:          files dns
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis

/etc/ldap.conf

###DEBCONF###
##
## Configuration of this file will be managed by debconf as long as the
## first line of the file says '###DEBCONF###'
##
## You should use dpkg-reconfigure to configure this file via debconf
##

#
# @(#)$Id: ldap.conf,v 1.38 2006/05/15 08:13:31 lukeh Exp $
#
# This is the configuration file for the LDAP nameservice
# switch library and the LDAP PAM module.
#
# PADL Software
# http://www.padl.com
#

# Your LDAP server. Must be resolvable without using LDAP.
# Multiple hosts may be specified, each separated by a
# space. How long nss_ldap takes to failover depends on
# whether your LDAP client library supports configurable
# network or connect timeouts (see bind_timelimit).
#host 127.0.0.1

# The distinguished name of the search base.
base dc=domain,dc=net

# Another way to specify your LDAP server is to provide an
uri ldap://ldap1.sc.domain.net
# Unix Domain Sockets to connect to a local LDAP Server.
#uri ldap://127.0.0.1/
#uri ldaps://127.0.0.1/
#uri ldapi://%2fvar%2frun%2fldapi_sock/
# Note: %2f encodes the '/' used as directory separator

# The LDAP version to use (defaults to 3
# if supported by client library)
ldap_version 3

# The distinguished name to bind to the server with.
# Optional: default is to bind anonymously.
#binddn cn=proxyuser,dc=padl,dc=com

# The credentials to bind with.
# Optional: default is no credential.
#bindpw secret

# The distinguished name to bind to the server with
# if the effective user ID is root. Password is
# stored in /etc/ldap.secret (mode 600)
#rootbinddn cn=manager,dc=padl,dc=com

# The port.
# Optional: default is 389.
#port 389

# The search scope.
#scope sub
#scope one
#scope base

# Search timelimit
#timelimit 30

# Bind/connect timelimit
#bind_timelimit 30

# Reconnect policy: hard (default) will retry connecting to
# the software with exponential backoff, soft will fail
# immediately.
#bind_policy hard

# Idle timelimit; client will close connections
# (nss_ldap only) if the server has not been contacted
# for the number of seconds specified below.
#idle_timelimit 3600

# Filter to AND with uid=%s
#pam_filter objectclass=account

# The user ID attribute (defaults to uid)
#pam_login_attribute uid

# Search the root DSE for the password policy (works
# with Netscape Directory Server)
#pam_lookup_policy yes

# Check the 'host' attribute for access control
# Default is no; if set to yes, and user has no
# value for the host attribute, and pam_ldap is
# configured for account management (authorization)
# then the user will not be allowed to login.
#pam_check_host_attr yes

# Check the 'authorizedService' attribute for access
# control
# Default is no; if set to yes, and the user has no
# value for the authorizedService attribute, and
# pam_ldap is configured for account management
# (authorization) then the user will not be allowed
# to login.
#pam_check_service_attr yes

# Group to enforce membership of
#pam_groupdn cn=PAM,ou=Groups,dc=padl,dc=com

# Group member attribute
#pam_member_attribute uniquemember

# Specify a minium or maximum UID number allowed
#pam_min_uid 0
#pam_max_uid 0

# Template login attribute, default template user
# (can be overriden by value of former attribute
# in user's entry)
#pam_login_attribute userPrincipalName
#pam_template_login_attribute uid
#pam_template_login nobody

# HEADS UP: the pam_crypt, pam_nds_passwd,
# and pam_ad_passwd options are no
# longer supported.
#
# Do not hash the password at all; presume
# the directory server will do it, if
# necessary. This is the default.
pam_password md5

# Hash password locally; required for University of
# Michigan LDAP server, and works with Netscape
# Directory Server if you're using the UNIX-Crypt
# hash mechanism and not using the NT Synchronization
# service.
#pam_password crypt

# Remove old password first, then update in
# cleartext. Necessary for use with Novell
# Directory Services (NDS)
#pam_password clear_remove_old
#pam_password nds

# RACF is an alias for the above. For use with
# IBM RACF
#pam_password racf

# Update Active Directory password, by
# creating Unicode password and updating
# unicodePwd attribute.
#pam_password ad

# Use the OpenLDAP password change
# extended operation to update the password.
#pam_password exop

# Redirect users to a URL or somesuch on password
# changes.
#pam_password_prohibit_message Please visit http://internal to change your password.

# RFC2307bis naming contexts
# Syntax:
# nss_base_XXX      base?scope?filter
# where scope is {base,one,sub}
# and filter is a filter to be &'d with the
# default filter.
# You can omit the suffix eg:
# nss_base_passwd   ou=People,
# to append the default base DN but this
# may incur a small performance impact.
#nss_base_passwd    ou=People,dc=padl,dc=com?one
#nss_base_shadow    ou=People,dc=padl,dc=com?one
#nss_base_group     ou=Group,dc=padl,dc=com?one
#nss_base_hosts     ou=Hosts,dc=padl,dc=com?one
#nss_base_services  ou=Services,dc=padl,dc=com?one
#nss_base_networks  ou=Networks,dc=padl,dc=com?one
#nss_base_protocols ou=Protocols,dc=padl,dc=com?one
#nss_base_rpc       ou=Rpc,dc=padl,dc=com?one
#nss_base_ethers    ou=Ethers,dc=padl,dc=com?one
#nss_base_netmasks  ou=Networks,dc=padl,dc=com?ne
#nss_base_bootparams    ou=Ethers,dc=padl,dc=com?one
#nss_base_aliases   ou=Aliases,dc=padl,dc=com?one
#nss_base_netgroup  ou=Netgroup,dc=padl,dc=com?one

# attribute/objectclass mapping
# Syntax:
#nss_map_attribute  rfc2307attribute    mapped_attribute
#nss_map_objectclass    rfc2307objectclass  mapped_objectclass

# configure --enable-nds is no longer supported.
# NDS mappings
#nss_map_attribute uniqueMember member

# Services for UNIX 3.5 mappings
#nss_map_objectclass posixAccount User
#nss_map_objectclass shadowAccount User
#nss_map_attribute uid msSFU30Name
#nss_map_attribute uniqueMember msSFU30PosixMember
#nss_map_attribute userPassword msSFU30Password
#nss_map_attribute homeDirectory msSFU30HomeDirectory
#nss_map_attribute homeDirectory msSFUHomeDirectory
#nss_map_objectclass posixGroup Group
#pam_login_attribute msSFU30Name
#pam_filter objectclass=User
#pam_password ad

# configure --enable-mssfu-schema is no longer supported.
# Services for UNIX 2.0 mappings
#nss_map_objectclass posixAccount User
#nss_map_objectclass shadowAccount user
#nss_map_attribute uid msSFUName
#nss_map_attribute uniqueMember posixMember
#nss_map_attribute userPassword msSFUPassword
#nss_map_attribute homeDirectory msSFUHomeDirectory
#nss_map_attribute shadowLastChange pwdLastSet
#nss_map_objectclass posixGroup Group
#nss_map_attribute cn msSFUName
#pam_login_attribute msSFUName
#pam_filter objectclass=User
#pam_password ad

# RFC 2307 (AD) mappings
#nss_map_objectclass posixAccount user
#nss_map_objectclass shadowAccount user
#nss_map_attribute uid sAMAccountName
#nss_map_attribute homeDirectory unixHomeDirectory
#nss_map_attribute shadowLastChange pwdLastSet
#nss_map_objectclass posixGroup group
#nss_map_attribute uniqueMember member
#pam_login_attribute sAMAccountName
#pam_filter objectclass=User
#pam_password ad

# configure --enable-authpassword is no longer supported
# AuthPassword mappings
#nss_map_attribute userPassword authPassword

# AIX SecureWay mappings
#nss_map_objectclass posixAccount aixAccount
#nss_base_passwd ou=aixaccount,?one
#nss_map_attribute uid userName
#nss_map_attribute gidNumber gid
#nss_map_attribute uidNumber uid
#nss_map_attribute userPassword passwordChar
#nss_map_objectclass posixGroup aixAccessGroup
#nss_base_group ou=aixgroup,?one
#nss_map_attribute cn groupName
#nss_map_attribute uniqueMember member
#pam_login_attribute userName
#pam_filter objectclass=aixAccount
#pam_password clear

# Netscape SDK LDAPS
#ssl on

# Netscape SDK SSL options
#sslpath /etc/ssl/certs

# OpenLDAP SSL mechanism
# start_tls mechanism uses the normal LDAP port, LDAPS typically 636
#ssl start_tls
#ssl on

# OpenLDAP SSL options
# Require and verify server certificate (yes/no)
# Default is to use libldap's default behavior, which can be configured in
# /etc/openldap/ldap.conf using the TLS_REQCERT setting.  The default for
# OpenLDAP 2.0 and earlier is "no", for 2.1 and later is "yes".
#tls_checkpeer yes

# CA certificates for server certificate verification
# At least one of these are required if tls_checkpeer is "yes"
#tls_cacertfile /etc/ssl/ca.cert
#tls_cacertdir /etc/ssl/certs

# Seed the PRNG if /dev/urandom is not provided
#tls_randfile /var/run/egd-pool

# SSL cipher suite
# See man ciphers for syntax
#tls_ciphers TLSv1

# Client certificate and key
# Use these, if your server requires client authentication.
#tls_cert
#tls_key

# Disable SASL security layers. This is needed for AD.
#sasl_secprops maxssf=0

# Override the default Kerberos ticket cache location.
#krb5_ccname FILE:/etc/.ldapcache

# SASL mechanism for PAM authentication - use is experimental
# at present and does not support password policy control
#pam_sasl_mech DIGEST-MD5

/etc/pam.d/common-session

# here are the per-package modules (the "Primary" block)
session [default=1]     pam_permit.so
# here's the fallback if no module succeeds
session requisite     pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
session required      pam_permit.so
# The pam_umask module will set the umask according to the system default in
# /etc/login.defs and user settings, solving the problem of different
# umask settings with different shells, display managers, remote sessions etc.
# See "man pam_umask".
session optional      pam_umask.so
# and here are more per-package modules (the "Additional" block)
session required  pam_unix.so
session optional      pam_ldap.so
# end of pam-auth-update config

session required    pam_mkhomedir.so skel=/etc/skel umask=0022

If i kill the ldap server and restart nscd so the cache isn't there I get long lookup times.

root@mongo1:~# /etc/init.d/nscd restart
* Restarting Name Service Cache Daemon nscd                            [ OK ]
root@mongo1:~# time id mike
^C

real 1m41.691s
user 0m0.004s
sys 0m0.004s

As you can see it took over a minute and I ctrl+c it. The user is in /etc/passwd also

share|improve this question
    
How much time does simple DNS name resolution work for cases when your LDAP server is up and when is down? –  jollyroger Nov 18 at 23:22
    
I don't think that "id mike" is a perfect test because that enumerates all groups the account belongs to (so will always query ldap for secondary groups). I'd hope that "id -un mike" would finish quickly (given you have SUCCESS=return). That still doesn't explain why nscd takes so long to notice that LDAP isn't available - have you tried turning on nscd debug and/or strace? –  Paul Haldane 2 days ago
    
Could use nscd.conf as well. Also might try changing pam_unix to sufficient instead of required and nsswitch's compat to files, but this should have the effect of file-derived users being fixed and only doing ldap checks on objects not in files. I suspect nscd is not smart enough to cache ldap server status; I think it only caches syscall results, but I would have to check the source--the docs are sparse. –  Andrew Domaszek 2 days ago

2 Answers 2

Have you tried setting those parameters in ldap.conf?

# Search timelimit
#timelimit 30

# Bind/connect timelimit
#bind_timelimit 30

# Reconnect policy: hard (default) will retry connecting to
# the software with exponential backoff, soft will fail
# immediately.
#bind_policy hard
share|improve this answer
    
Yes I set network_timeout, timelimit, bind_timelimit and timeout to 1. It still takes several seconds to complete a single LDAP request. The command ls -l still takes minutes. –  fr00tyl00p Nov 18 at 18:01

That problem is usually solved by extra caching layers like PAM ccreds or more advanced solution like RHEL's sssd . For pam ccreds the config file /etc/pam.d/common-auth will be somewhat like

auth sufficient /lib/security/pam_unix.so
auth [authinfo_unavail=ignore success=1 default=2] /lib/security/pam_ldap.so use_first_pass
auth [default=done]     /lib/security/pam_ccreds.so action=validate use_first_pass
auth [default=done]     /lib/security/pam_ccreds.so action=store
auth [default=bad]      /lib/security/pam_ccreds.so action=update

Also, if you don't care about accounts stored in ldap, authinfo_unavail=ignore may help on it's own too. Although I'm not 100% sure that nscd does not use query LDAP for other purpose.

share|improve this answer
    
ccreds did it :-) Thanks !! –  fr00tyl00p yesterday

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