1. Introduction

    System Information

  2. Inter-Process Communication
  3. Signals

    Programming in Various Environments

  4. Script Programming
    1. Script Variables
    2. Test Conditions
    3. Control and Iteration
    4. Commonly used Programs
    5. Shell Capabilities
    6. Example looping script
    7. Example using Variables
    8. Example working with files
    9. Example install script
  5. C and C++ Programming
    1. POSIX System Capabilities
    2. More POSIX
    3. Threads
    4. Mutexes
    5. An example viewmod program
    6. An example serial program
  6. X Programming
  7. Debugging
  8. Credits

Linux Signals

Signals

Linux Signals are:

Signal NameNumberDescription
SIGHUP1Hangup (POSIX)
SIGINT2Terminal interrupt (ANSI)
SIGQUIT3Terminal quit (POSIX)
SIGILL4Illegal instruction (ANSI)
SIGTRAP5Trace trap (POSIX)
SIGIOT6IOT Trap (4.2 BSD)
SIGBUS7BUS error (4.2 BSD)
SIGFPE8Floating point exception (ANSI)
SIGKILL9Kill(can't be caught or ignored) (POSIX)
SIGUSR110User defined signal 1 (POSIX)
SIGSEGV11Invalid memory segment access (ANSI)
SIGUSR212User defined signal 2 (POSIX)
SIGPIPE13Write on a pipe with no reader, Broken pipe (POSIX)
SIGALRM14Alarm clock (POSIX)
SIGTERM15Termination (ANSI)
SIGSTKFLT16Stack fault
SIGCHLD17Child process has stopped or exited, changed (POSIX)
SIGCONT18 Continue executing, if stopped (POSIX)
SIGSTOP19Stop executing(can't be caught or ignored) (POSIX)
SIGTSTP20Terminal stop signal (POSIX)
SIGTTIN21Background process trying to read, from TTY (POSIX)
SIGTTOU22Background process trying to write, to TTY (POSIX)
SIGURG23Urgent condition on socket (4.2 BSD)
SIGXCPU24CPU limit exceeded (4.2 BSD)
SIGXFSZ25File size limit exceeded (4.2 BSD)
SIGVTALRM26Virtual alarm clock (4.2 BSD)
SIGPROF27Profiling alarm clock (4.2 BSD)
SIGWINCH28Window size change (4.3 BSD, Sun)
SIGIO29I/O now possible (4.2 BSD)
SIGPWR30Power failure restart (System V)

As noted above, processes can ignore, block, or catch all signals except SIGSTOP and SIGKILL. If a process catches a signal, it means that it includes code that will take appropriate action when the signal is received. If the signal is not caught by the process, the kernel will take default action for the signal.

FIFOs

FIFOs are permanent objects and can be created using the mkfifo(1) or mknod(1) command. Inside the program, the FIFO can be created using the mknod command, then opened and read from or written to just like a normal file. The FIFO is normally in blocking mode when attempting to perform read operations.