Hey what is daemon and processes…
Daemons and Processes:
Q1. What are applications daemons?
Application Daemon are those which can be killed & will have no effect to the system
$ kill -15 <appd-pid>
For eg. – firefox, openoffice, X server, etc…
Q2. What are system daemons?
System Daemons are those which can be killed & will affect the system.
$ kill -9 <sysd-pid>
For eg – init, kerneld, ksoftirqd, khelper, kthread, kblockd
Q3. What is a Process?
Processes carry out tasks within the operating system. A process has many components and properties.
Q4. What are signals in linux?
Signals are a software mechanism that are similar to a message of some
sort. They can be trapped and handled or ignored
Signals operate through two different system calls
1) The kill system call
2) The signal system call
1) The kill System Call
The kill system call sends a signal to a process kill is generally used to
terminate a process. It requires the PID of the process to be terminated
and the signal number to send as arguments.
2) The Signal System Call
The signal system call is much more diverse. When a signal occurs, the
kernel checks to see if the user had executed a signal system call and was
therefor expecting a signal. If the call was to ignore the signal, the
Otherwise, it checks to see if it was a trap or kill signal If not, it
processes the signal If it was a trap or kill signal, the kernel checks to
see if core should be dumped and then calls the exit routine to terminate
the user process.
Common Unix Signals
SIGINS Illegal Instruction
SIGTRAP Trace Trap
SIGSYS Bad argument to system call
SIGPIPE Write on pipe with no one to read it
SIGTERM Software termination signal from kill
SIGSTOP Stop signal