Advanced Programming in UNIX environment-daemon list & signal description list

1. Daemon list

AMD: Automatic Installation of NFS (Network File System) Guard process apmd: Advanced Power governance arpwatch: record logs and build an ethernet address and IP address on the LAN interface to the database autofs: automatic Installation of the management process automount, associated with NFS, relies on nisbootparamd: boot parameter server to provide information required for boot for diskless workstation on the LAN crond: schedule task DHCPD in Linux: start a DHCP (Dynamic IP Address Allocation) server gated: Gateway route waiting process, use the dynamic OSPF route selection protocol httpd: Web Server inetd: supports multiple network services core waiting program innd: usenet news server linuxconf: promised to use the local web server as the user interface to configure the machine LPD: print the server Mars-nwe: Mars-nwe file and the printing server mcserv for Novell: midnight command file server named: DNS server netfs: Install NFS, Samba, and Netware Network File System Network: Activate the script program NFS with configured network interfaces: Open NFS service nscd: the nscd (name switch cache Daemon) server is used as a support service for NIS. It caches user passwords and forms a membership relationship Portmap: RPC Portmap controller, similar to inetd, it manages RPC-based connection to PostgreSQL: A sqldatabase server routed: routing waiting process, using the dynamic rip route selection protocol rstatd: A waiting program for other machines on the LAN to collect and provide system information ruserd: remote user location service, which is an RPC-based service, it provides user information about the logs currently recorded on a machine on the LAN. Rwalld: activates RPC. rwall service process. This is an RPC-based service that allows users to write messages to other terminals registered on the LAN machine. rwhod: activates the rwhod service process, it supports the rwho and ruptime services of LAN Sendmail: Mail Server sendmailsmb: Samba file sharing/printing service snmpd: Local simple network governance process squid: Activate the proxy server squidsyslog: A script XFS: X Window server that enables Syslog and klogd system logs to wait for processes during system boot, providing xntpd: Network Time Server ypbind for local and remote X servers: activate ypbind service process yppasswdd: NIS Password server ypserv: NIS master server GPM: mouse-over identd: AUTH service for NIS (Network Information System) clients, similar to finger in providing user information 2. Signal description list

$ kill -l1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL5) SIGTRAP      6) SIGABRT      7) SIGBUS       8) SIGFPE9) SIGKILL     10) SIGUSR1     11) SIGSEGV     12) SIGUSR213) SIGPIPE     14) SIGALRM     15) SIGTERM     16) SIGSTKFLT 17) SIGCHLD18) SIGCONT     19) SIGSTOP     20) SIGTSTP     21) SIGTTIN22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ26) SIGVTALRM   27) SIGPROF     28) SIGWINCH    29) SIGIO30) SIGPWR      31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+136) SIGRTMIN+2  37) SIGRTMIN+3  38) SIGRTMIN+4  39) SIGRTMIN+540) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8  43) SIGRTMIN+944) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+1348) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-1352) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-956) SIGRTMAX-8  57) SIGRTMAX-7  58) SIGRTMAX-6  59) SIGRTMAX-560) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2  63) SIGRTMAX-164) SIGRTMAX

List, numbered 1 ~ The 31 signal is a traditional Unix-supported signal, which is an unreliable signal (non-real-time) numbered 32 ~ The 63 signal was expanded later, called a reliable signal (real-time signal ). The difference between unreliable and reliable signals is that the former does not support queuing and may cause signal loss, while the latter does not.

Below we will discuss the signal number smaller than sigrtmin.

1) sighup
This signal is sent at the end of the user terminal connection (normal or abnormal). Generally, when the control process of the terminal ends, it notifies all jobs in the same session, they are no longer associated with control terminals.
When you log on to Linux, the system assigns a session to the login user ). All programs running on this terminal, including foreground and background process groups, generally belong to this session. When you log out of Linux, processes in the frontend process group and in the background that are output to the terminal will receive a sighup signal. The default operation for this signal is to terminate the process. Therefore, the Process with terminal output in the frontend and backend will be aborted. However, this signal can be captured. For example, wget can capture the sighup signal and ignore it. In this way, even if you log out of Linux, wget can continue downloading.
In addition, this signal is used to notify the daemon that is out of the relationship with the terminal to re-read the configuration file.

 
2) SIGINT
The interrupt signal is sent when you type the intr character (usually Ctrl-C) to notify the foreground process group to terminate the process.

 

3) sigquit
Similar to SIGINT, but controlled by the quit character (usually Ctrl-/). A process generates a core file when it exits because it receives sigquit, which is similar to a program error signal.

 

4) sigill
The execution of invalid commands is usually caused by errors in the executable file, or the attempt to execute data segment. Stack Overflow may also generate this signal.

 

5) sigtrap
Generated by breakpoint commands or other trap commands. Used by debugger.

 

6) SIGABRT
The signal generated by calling the abort function.

 

7) sigbus
Invalid Address, including memory address alignment error. For example, you can access an integer with four characters in length, but its address is not a multiple of 4. It differs from SIGSEGV in that the latter is triggered by illegal access to valid storage addresses (for example, access does not belong to your own bucket or read-only bucket ).

 

8) sigfpe
When a fatal arithmetic operation error occurs, it includes not only floating point operation errors, but also overflow and Division 0 and other arithmetic errors.

 

9) sigkill
It is used to immediately end the running of the program. This signal cannot be blocked, processed, or ignored. If the Administrator finds that a process cannot be terminated, he can try to send this signal.

 

10) SIGUSR1
Reserved for users

 

11) SIGSEGV
Try to access the memory not allocated to you, or try to write data to the memory address that has no write permission.

 

12) sigusr2
Reserved for users

 

13) sigpipe
Pipe rupture. This signal is usually generated during inter-process communication. For example, for two processes that use FIFO (pipeline) Communication, the read pipeline is written to the pipeline if it is not opened or unexpectedly terminated, and the write process receives the sigpipe signal. In addition, when writing a socket to two processes that communicate with a socket, the read process is terminated.

 

14) sigalrm
The scheduled clock signal is used to calculate the actual time or clock time. The alarm function uses this signal.

 

15) sigterm
The program terminate signal. Unlike sigkill, the signal can be blocked and processed. It is usually used to require the program to exit normally. The shell command kill generates this signal by default. If the process cannot be terminated, we will try sigkill.

 

17) sigchld
When the child process ends, the parent process receives this signal.
If the parent process does not process this signal and does not wait for the child process (wait), although the child process terminates, it still occupies a table item in the kernel table, at this time, sub-processes are called Zombie processes. In this situation, we should avoid (parent process, ignore sigchild signal, capture it, or wait, its derived child process, or the parent process is terminated first, at this time, the termination of the sub-process is automatically taken over by the INIT process ).

 

18) sigcont
Let a stopped process continue to execute. This signal cannot be blocked. You can use a handler to allow the program to complete specific work when the stopped status changes to continue execution.
For example, re-display the prompt...

 

19) sigstop
Stop (stopped) process execution. Note the difference between it and terminate and interrupt: the process has not ended, but is paused. This signal cannot be blocked, processed, or ignored.

 

20) sigtstp
The process is stopped, but the signal can be processed and ignored. This signal is sent when you type the susp character (usually Ctrl-Z ).

 

21) sigttin
When a background job reads data from a user terminal, all processes in the job receive the sigttin signal.

 

22) sigttou
Similar to sigttin, but received when writing terminal (or modifying terminal mode.

 

23) sigurg
"Urgent" data or out-of-band data is generated when it reaches the socket.

 

24) sigxcpu
The CPU time limit is exceeded. This limit can be read/changed by getrlimit/setrlimit.

 

25) sigxfsz
When a process attempts to expand a file so that it exceeds the file size resource limit.

 

26) sigvtalrm
The virtual clock signal is similar to sigalrm, but the CPU time occupied by the process is calculated.

 

27) sigprof
Similar to sigalrm/sigvtalrm, but includes the CPU time used by the process and the time when the system calls it.

 

28) sigwinch
Window size changed.

 

29) sigio
The file descriptor is ready for input/output operations.

 

30) sigpwr
Power failure

 

31) sigsys
Invalid system call.

 

In the Signals listed above:

Signals that cannot be captured, blocked, or ignored by programs include: sigkill and sigstop.
Signals that cannot be restored to the default action include sigill and sigtrap, which by default will lead to process abortion: SIGABRT, sigbus, sigfpe, sigill, sigiot, sigquit, SIGSEGV, sigtrap, sigxcpu, by default, sigxfsz causes the process to exit by signal sigalrm, sighup, SIGINT, sigkill, sigpipe, sigpoll, sigprof, sigsys, sigterm, SIGUSR1, sigusr2, by default, sigvtalrm will cause the process to stop. The following signals are ignored by the default processes: sigstop, sigtstp, sigttin, and sigttou: sigchld, sigpwr, sigurg, and sigwinch.

In addition, sigio exits in svr4 and is ignored in 4.3bsd; sigcont continues when the process is suspended; otherwise, it is ignored and cannot be blocked.

$ kill -l1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL5) SIGTRAP      6) SIGABRT      7) SIGBUS       8) SIGFPE9) SIGKILL     10) SIGUSR1     11) SIGSEGV     12) SIGUSR213) SIGPIPE     14) SIGALRM     15) SIGTERM     16) SIGSTKFLT 17) SIGCHLD18) SIGCONT     19) SIGSTOP     20) SIGTSTP     21) SIGTTIN22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ26) SIGVTALRM   27) SIGPROF     28) SIGWINCH    29) SIGIO30) SIGPWR      31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+136) SIGRTMIN+2  37) SIGRTMIN+3  38) SIGRTMIN+4  39) SIGRTMIN+540) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8  43) SIGRTMIN+944) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+1348) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-1352) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-956) SIGRTMAX-8  57) SIGRTMAX-7  58) SIGRTMAX-6  59) SIGRTMAX-560) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2  63) SIGRTMAX-164) SIGRTMAX

List, numbered 1 ~ The 31 signal is a traditional Unix-supported signal, which is an unreliable signal (non-real-time) numbered 32 ~ The 63 signal was expanded later, called a reliable signal (real-time signal ). The difference between unreliable and reliable signals is that the former does not support queuing and may cause signal loss, while the latter does not.

Below we will discuss the signal number smaller than sigrtmin.

1) sighup
This signal is sent at the end of the user terminal connection (normal or abnormal). Generally, when the control process of the terminal ends, it notifies all jobs in the same session, they are no longer associated with control terminals.
When you log on to Linux, the system assigns a session to the login user ). All programs running on this terminal, including foreground and background process groups, generally belong to this session. When you log out of Linux, processes in the frontend process group and in the background that are output to the terminal will receive a sighup signal. The default operation for this signal is to terminate the process. Therefore, the Process with terminal output in the frontend and backend will be aborted. However, this signal can be captured. For example, wget can capture the sighup signal and ignore it. In this way, even if you log out of Linux, wget can continue downloading.
In addition, this signal is used to notify the daemon that is out of the relationship with the terminal to re-read the configuration file.

 
2) SIGINT
The interrupt signal is sent when you type the intr character (usually Ctrl-C) to notify the foreground process group to terminate the process.

 

3) sigquit
Similar to SIGINT, but controlled by the quit character (usually Ctrl-/). A process generates a core file when it exits because it receives sigquit, which is similar to a program error signal.

 

4) sigill
The execution of invalid commands is usually caused by errors in the executable file, or the attempt to execute data segment. Stack Overflow may also generate this signal.

 

5) sigtrap
Generated by breakpoint commands or other trap commands. Used by debugger.

 

6) SIGABRT
The signal generated by calling the abort function.

 

7) sigbus
Invalid Address, including memory address alignment error. For example, you can access an integer with four characters in length, but its address is not a multiple of 4. It differs from SIGSEGV in that the latter is triggered by illegal access to valid storage addresses (for example, access does not belong to your own bucket or read-only bucket ).

 

8) sigfpe
When a fatal arithmetic operation error occurs, it includes not only floating point operation errors, but also overflow and Division 0 and other arithmetic errors.

 

9) sigkill
It is used to immediately end the running of the program. This signal cannot be blocked, processed, or ignored. If the Administrator finds that a process cannot be terminated, he can try to send this signal.

 

10) SIGUSR1
Reserved for users

 

11) SIGSEGV
Try to access the memory not allocated to you, or try to write data to the memory address that has no write permission.

 

12) sigusr2
Reserved for users

 

13) sigpipe
Pipe rupture. This signal is usually generated during inter-process communication. For example, for two processes that use FIFO (pipeline) Communication, the read pipeline is written to the pipeline if it is not opened or unexpectedly terminated, and the write process receives the sigpipe signal. In addition, when writing a socket to two processes that communicate with a socket, the read process is terminated.

 

14) sigalrm
The scheduled clock signal is used to calculate the actual time or clock time. The alarm function uses this signal.

 

15) sigterm
The program terminate signal. Unlike sigkill, the signal can be blocked and processed. It is usually used to require the program to exit normally. The shell command kill generates this signal by default. If the process cannot be terminated, we will try sigkill.

 

17) sigchld
When the child process ends, the parent process receives this signal.
If the parent process does not process this signal and does not wait for the child process (wait), although the child process terminates, it still occupies a table item in the kernel table, at this time, sub-processes are called Zombie processes. In this situation, we should avoid (parent process, ignore sigchild signal, capture it, or wait, its derived child process, or the parent process is terminated first, at this time, the termination of the sub-process is automatically taken over by the INIT process ).

 

18) sigcont
Let a stopped process continue to execute. This signal cannot be blocked. You can use a handler to allow the program to complete specific work when the stopped status changes to continue execution.
For example, re-display the prompt...

 

19) sigstop
Stop (stopped) process execution. Note the difference between it and terminate and interrupt: the process has not ended, but is paused. This signal cannot be blocked, processed, or ignored.

 

20) sigtstp
The process is stopped, but the signal can be processed and ignored. This signal is sent when you type the susp character (usually Ctrl-Z ).

 

21) sigttin
When a background job reads data from a user terminal, all processes in the job receive the sigttin signal.

 

22) sigttou
Similar to sigttin, but received when writing terminal (or modifying terminal mode.

 

23) sigurg
"Urgent" data or out-of-band data is generated when it reaches the socket.

 

24) sigxcpu
The CPU time limit is exceeded. This limit can be read/changed by getrlimit/setrlimit.

 

25) sigxfsz
When a process attempts to expand a file so that it exceeds the file size resource limit.

 

26) sigvtalrm
The virtual clock signal is similar to sigalrm, but the CPU time occupied by the process is calculated.

 

27) sigprof
Similar to sigalrm/sigvtalrm, but includes the CPU time used by the process and the time when the system calls it.

 

28) sigwinch
Window size changed.

 

29) sigio
The file descriptor is ready for input/output operations.

 

30) sigpwr
Power failure

 

31) sigsys
Invalid system call.

 

In the Signals listed above:

Signals that cannot be captured, blocked, or ignored by programs include: sigkill and sigstop.
Signals that cannot be restored to the default action include sigill and sigtrap, which by default will lead to process abortion: SIGABRT, sigbus, sigfpe, sigill, sigiot, sigquit, SIGSEGV, sigtrap, sigxcpu, by default, sigxfsz causes the process to exit by signal sigalrm, sighup, SIGINT, sigkill, sigpipe, sigpoll, sigprof, sigsys, sigterm, SIGUSR1, sigusr2, by default, sigvtalrm will cause the process to stop. The following signals are ignored by the default processes: sigstop, sigtstp, sigttin, and sigttou: sigchld, sigpwr, sigurg, and sigwinch.

In addition, sigio exits in svr4 and is ignored in 4.3bsd; sigcont continues when the process is suspended; otherwise, it is ignored and cannot be blocked.