(http://www.yolinux.com/TUTORIALS/LinuxTutorialSysAdmin.html)
User limitations are set in the following files:
    * File: /etc/security/limits.conf :
          o core – limits the core file size (KB)
          o data – max data size (KB)
          o fsize – maximum filesize (KB)
          o memlock – max locked-in-memory address space (KB)
          o nofile – max number of open files
          o rss – max resident set size (KB)
          o stack – max stack size (KB)
          o cpu – max CPU time (MIN)
          o nproc – max number of processes
          o as – address space limit
          o maxlogins – max number of logins for this user
          o priority – the priority to run user process with
          o locks – max number of file locks the user can hold     * File: /etc/security/access.conf :
      Limit access by network or local console logins.
    * File: /etc/security/group.conf :
      Grant/restrict group device access.
      Also see the YoLinux tutorial on Managing groups
    * File: /etc/security/time.conf :
      Restrict user access by time, day. 
Also see:
    * Set user quotas on hard drive usage – YoLinux Tutorial
    * bash shell command ulimit. (Mentioned above)
    * getrlimit, getrusage, setrlimit – get/set resource limits and usage (C programmer api)
    * sysconf – Get configuration information at runtime (C programmer api) 

