Working with the Unix OS

struct timeval {
long tv_sec; /* seconds since 00:00:00 GMT, 1 Jan 1970 */
long tv_usec; /* and microseconds */
};
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Processes I
If the "stick bit" is set, the executable program's read-only text is left in swap, so that it will start faster next time.
! File Mode creation Mask
int umask(int mask)
(This is one of the few system calls that cannot fail and does not have an error return
{exit, getpid, getpgrp, getppid, getuid,
geteuid, getgid, getegid, umask})
The file creation mask is used when a new file or directory is created. The mask specifies which bits in the new
file are to cleared. If the file mode creation mask is octal 022, the group-write bit is off giving an actual mode of
octal 0644.
! Major and Minor Device Numbers
For disk drives the major number usually specifies the disk controller and the minor number specifies both the drive
and the partition on the drive.
For example a controller that supports up to 8 drives can use minor device numbers 0-7 for up to 8 partitions on
the first drive, 8-15 for partitions on the second drive, and so on.
! Directories
int mkdir(char *pathname, int mode); /* 14 byte name, 2 byte mode */
int system(char *string);
char buff[1024], dirname[1024];
sprintf(buff, "mkdir %s", dirname);
if (system(buff) != 0) {
/* error handling */
}
! Current Working Directory
Each process has associated with it a cwd. A process can change its cwd with chdir.
int chdir(char *pathname);
! Process Group ID
Every process is a member of a process group. It is possible to send a signal using the kill system call to all
processes belonging to a specified process group.
The value of the process group ID is obtained by calling getpgrp system call. Under System V a process is only
able to change its process group ID to be equal to its process ID, effectively becoming a process group leader.
int setpgrp();
! Terminal Group ID and Control Terminal
Each process can be a member of a terminal group. The terminal group ID is the process ID of the process group
leader that opened the terminal.
The terminal group ID identifies the control terminal for a process group. When the process group leader for a
terminal calls exit, a hangup signal is sent to each process in the process group.
! Socket Group ID
BSD supports the notion of a process group of sockets. Each socket that is open has a socket group ID.
! Time-of-Day
BSD provides gettimeofday system call
#include
int gettimeofday(struct timval *tvalptr, struct timezone *tzoneptr);