遇到 openldap 的问题，我从来没有成功解决过。我们在另一台机器上运行 openldap，它有自己的 vlan。现在，如果该 ldap 服务器死机，任何访问 uid 或 gid 的东西似乎都会陷入停滞，直到发生超时。
这是我的
/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
如果我关闭 ldap 服务器并重新启动 nscd，那么缓存就不存在了，查找时间就会很长。
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
你可以看到它花了一分钟多的时间，然后我按 ctrl+c 键。用户也在 /etc/passwd 中
答案1
该问题通常通过额外的缓存层（如 PAM ccreds）或更高级的解决方案（如 RHEL 的 sssd）来解决。对于 pam ccreds，配置文件/etc/pam.d/common-auth将类似于
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
另外，如果您不关心存储在 ldap 中的帐户，authinfo_unavail=ignore它本身也可能有帮助。虽然我不能 100% 确定 nscd 不会将查询 LDAP 用于其他目的。
答案2
您是否尝试过在 ldap.conf 中设置这些参数？
# 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