setpgrp(creates new process group by calling the system call setpgrp(or setpgrp( )depending on which version is implemented (if anyreturns the id of the new process group (unixsetpgid(pidpgrpassigns process pid to process group pgrp if pid is equal to pgrpthe process becomes new process group leader if pid is not equal to pgrpthe process joins an existing group if pid is the process id of the calling process is used if pgrp is the process specified by pid becomes process group leader (unixsetreuid(ruid,euidsets the real and effective user id of the calling process (unixsetregid(rgid,egidsets the real and effective group id of the calling process (unixsetsid(creates new session and returns the newly created session id sessions are typically associated with terminal devices and the job control of processes that are started within them (unixsetuid(uidsets the real user id of the current process this function is privileged and often can be performed only by processes running as root (unixstrerror(codereturns the error message corresponding to the integer error code (unix and windowsthe errno module defines symbolic names for these error codes umask(masksets the current numeric umask and returns the previous umask the umask is used to clear permissions bits on files that are created by the process (unix and windowsuname(returns tuple of strings (sysnamenodenamereleaseversionmachineidentifying the system type (unixunsetenv(nameunsets the environment variable name file creation and file descriptors the following functions provide low-level interface for manipulating files and pipes in these functionsfiles are manipulated in terms of an integer file descriptorfd the file descriptor can be extracted from file object by invoking its fileno(method close(fdcloses the file descriptor fd previously returned by open(or pipe( lib fl ff