Configuring PAM Authenticator

The HPE Ezmeral Data Fabric supports Pluggable Authentication Modules (PAM) in the UNIX authentication stack. HPE Ezmeral Data Fabric provides a PAM Authenticator module that generates data-fabric tickets in conjunction with the maprlogin utility. After you install the platform, the PAM Authenticator module is located at $INSTALL_DIR/lib/libmapr_pam.so. Configuration files for PAM are located in the /etc/pam.d directory. Each UNIX operation, such as su, login, or ssh, has a specific PAM configuration file in that directory.

Configure the PAM Authenticator on Ubuntu or SLES

To configure the PAM Authenticator, append the following line to the end of the /etc/pam.d/common-auth file:

auth optional /opt/mapr/lib/libmapr_pam.so # MapR PAM module

WARNING
An absolute path to the location of the libmapr_pam.so file is required. By default, this location is $MAPR_HOME/lib/libmapr_pam.so.

Configure the PAM Authenticator on RHEL or CentOS

  1. Insert the following line in the /etc/pam.d/system-auth file immediately before the first module that uses the auth sufficient configuration: 
    auth optional libmapr_pam.so # MapR PAM module
  2. Append the string try_first_pass to the end of the module that uses auth sufficient, as in this example:

    Before modification:

    auth required pam_env.so
auth sufficient pam_unix.so nullok
auth requisite pam_succeed_if.so uid >= 500 quiet
auth required pam_deny.so
    After modification, changes in bold:
    auth required pam_env.so
auth optional libmapr_pam.so # MapR PAM module
auth sufficient pam_unix.so nullok try_first_pass
auth requisite pam_succeed_if.so uid >= 500 quiet
auth required pam_deny.so

Enable Debugging for PAM

To enable debugging for the client traffic used by the maprlogin utility, update the /opt/mapr/conf/log4j.properties file with the following line:

log4j.logger.com.mapr.login=DEBUG

After updating the log4j.properties file, trace the com.mapr.login package at the DEBUG level.

Be sure to update the correct instance of the log4j.properties file. Traffic specific to HPE Ezmeral Data Fabric, such as maprlogin and Control System traffic, uses the instance in the /opt/mapr/conf directory. Hadoop applications use the log4j.properties file in the /opt/mapr/hadoop/hadoop-2.x.x/etc/hadoop directory.

To perform the same tracing activity on the server side, modify the appropriate instance of the log4j.properties file on the server. Alternatively, specify the page com.mapr.login in the Control System UI's tracing/logger settings. To trace PAM activity from the server, add the following line to the server's log4j.properties instance:

log4j.logger.net.sf.jpam=DEBUG

After modifying this setting, the server log will contain a message similar to the following:

2013-07-23 16:05:25,200 DEBUG Pam [1068409264@qtp-874242484-3]: Debug mode active.

Detailed information about PAM activity is written to the /opt/mapr/logs/pam_<username>.log where username is the user name that Linux reports in response to the getpwuid(geteuid()) call for the process. In this case, Linux returns the effective user ID, which can be different from the real user ID or saved user ID. For more information, see Difference between Real User ID, Effective User ID and Saved User ID.

Other Packages

The following packages are not directly related to PAM, but can provide useful insights for subtler errors.

  • org.apache.hadoop.security - This package contains Apache security code, including HPE Ezmeral Data Fabric enhancements. Tracing this package can provide information about what login configuration is in use.

  • com.mapr.fs.cldb.http.login - This package contains code that the CLDB uses to validate maprlogin calls.

Common Issues

The Linux Documentation Project's HOWTO on LDAP Implementation has a section on PAM and NSS that may prove helpful.

If a user's credentials appear valid, for example where the su and ssh commands work normally but PAM does not correctly authenticate, the issue may relate specifically to HPE Ezmeral Data Fabric's use of PAM as a normal user. PAM consumers run as the root user, causing permissions issues. The two most common issues relating to this condition are:

  • The /etc/shadow directory is not readable to the mapr user. This directory is made readable to the mapr user during install, but some secure environments and configuration management tools undo these changes.

  • A Kerberos PAM module is attempting to create and change the ownership of a Kerberos ticket file. This attempt fails, since these changes require root privileges. Different Kerberos PAM modules can report errors differently, leading to difficulty tracking down root causes of errors. To address permissions problems with Kerberos PAM modules, configure the Kerberos PAM module to skip creating a ticket file, using the KDC only to validate the password. PAM configuration information is located in the /etc/pam.d directory. HPE Ezmeral Data Fabric can use a custom PAM configuration specified in the web.conf file.