Signals

In the early days of computing, signals were a means to deal with unusual events, and usually, their job was to reset a condition to a default state. Nowadays, with facilities such as job control, signals are used to actually instruct processes on what to do and are now more an interprocess facilities than a reset mechanism, as they were originally conceived. Each signal is associated to an action that must be performed by the process receiving it, so here is a brief list with some of the more interesting that the kernel can send to a process:

• SIGCHLD: This signal is sent to a parent process a child terminates or stops.
• SIGCONT: This tells the process that has put on hold by SIGSTOP or SGSTP to resume its execution. These three signals are used in job controlling.
• SIGHUP: This signal is sent to a when its terminal is closed and kills it. It owes its name to the old good times when connections were held over serial line, which hang up due to a line drop. If sent to a daemon, it usually...