6.11. Summary

The password file and the group file are used on all UNIX systems. We've looked at the various functions that read these files. We've also talked about shadow passwords, which can help system security. Supplementary group IDs provide a way to participate in multiple groups at the same time. We also looked at how similar functions are provided by most systems to access other system-related data files. We discussed the POSIX.1 functions that programs can use to identify the system on which they are running. We finished the chapter with a look at the time and date functions provided by ISO C and the Single UNIX Specification.