libc.a library provides functions that allow
the entry points into the kernel to be accessed just like local
functions.
access:
checks if calling process has file access
alarm:
sets a process's alarm clock
chdir:
changes the working directory
chmod:
changes the mode of a file
chown:
changes the ownership of a file
chroot:
changes the root directory
close:
closes a file descriptor
dup, dup2:
duplicates an open file descriptor
execl, execv, execle,
execve, execlp, execvp:
executes a file
exit:
exits a process
fcntl:
controls open files
fork:
creates a new process
getpid, getpgrp, getppid:
gets group and process IDs
getuid, geteuid, getgid,
getegid:
gets user and group IDs
ioctl:
controls character devices
kill:
sends a signal to one or more processes
link:
links a new file name to an existing file
lseek:
moves read/write file pointer
mknod:
makes a directory, special or ordinary file
mount:
mounts a filesystem
msgctl, msgget, msgsnd,
msgrcv:
message passing support
nice:
changes priority of a process
open:
opens a file for reading or writing
pause:
suspends a process until a signal occurs
pipe:
creates an interprocess pipe
plock:
locks a process in memory
profil:
requests an execution profile
ptrace:
allows a process to trace the execution of another
read:
reads from a file
semctl, semget, semop:
semaphore support
setpgrp:
sets process group ID
setuid, setgid:
sets user and group IDs
shmctl, shmget, shmop:
shared memory support
signal:
control of signal processing
sleep:
suspends execution for an interval
stat, fstat:
gets file status
stime:
sets the time
sync:
updates the super block
time:
number of seconds since 1/1/1970
times:
gets process and child process times
ulimit:
gets and sets user limits
umask:
gets and sets file creation mask
umount:
unmounts a file system
uname:
gets system information
unlink:
removes directory entry
ustat:
gets file system statistics
utime:
sets file access and modification times
wait:
waits for a child process to stop or terminate
write:
writes to a file
errno.
void perror(char *user_message)
Exercises
nice() system call.
Print out the resultant error number and associated error message.
Exam Style Questions