unix system interface programming part 6.3 – process and signal prepared by xu zhenya(...

Unix System Interface Unix System Interface ProgrammingProgramming

Part 6.3 – Process and Signal

Prepared by Xu Zhenya( [email protected] )

Draft – Xu Zhenya( 2002/10/01 )

Rev1.0 – Xu Zhenya( 2002/10/10 )

Unix Programming Environment Unix Programming Environment Dept. of CSE, BUAADept. of CSE, BUAA

AgendaAgenda 1. Process 1. Process

2. Signal2. Signal


Modeling the Concepts( Relationship )Modeling the Concepts( Relationship )

Controlling Terminal

Process Group

Current

Session

foreground

Background

Process

Parent1

1..n

+BelongTo

1

1..n

Leader

UserGroup

User

euid

11

Supplementary

ruid

saved_euid


Modeling the Concepts ( Sequence )Modeling the Concepts ( Sequence )

fork()

Parent Child

exec()

exit()abort()

Notification by SIGCHLDZombie

• The parent ignores/catches SIGCHLD.

• The parent = “init”

wait(), waitpid(), wait3(), wait4()


Process ContextProcess Context

kernel code/data/stack

Memory mapped region for shared libraries

runtime heap (via malloc)

program text (.text)

initialized data (.data)

uninitialized data (.bss)

stack

forbidden

0

%espprocess VM

brk

0xc0

physical memory

process-specific datastructures

(page tables,task and mm structs)

kernel VM

.data.text

p

demand-zero

demand-zero

libc.so

.data.text


Overview of “Process”Overview of “Process”CATEGORY FUNCTION

NAMEPURPOSE

Basic Primitives

fork(2) Create a new process

exec(2)execl(2)execv(2)execle(2)execve(2)execlp(2)execvp(2)

Execute a program

exit(2)_exit(2)

Terminate a process

wait(2)waitpid(2)wait3(2)wait4(2)

Wait for a child process to stop or terminate

waitid(2) Wait for a child process to change state

priocntl(2) Control process scheduler

nice(2) Change priority of a process

pause(2) Suspend process until signal

getcontext(2)setcontext(2)

Get and set current user context


Overview of “Process”Overview of “Process”

IDENTIFICATION

setuid(2)setgid(2)

SET USER AND GROUP IDS

getuid(2)geteuid(2)getgid(2)getegid(2)

Get real user, effective user, real group, and effective group IDs

getgroups(2)setgroups(2)

Get or set supplementary group access list IDs

Relationships

getpid(2)getpgrp(2)getppid(2)getpgid(2)

Get process, process group, and parent process IDs

setpgrp(2) Set process group ID

setpgid(2) Set process group ID

setsid(2) Set session ID

File System

chdir(2)fchdir(2)

Change working directory

chroot(2) Change root directory

Runtime Linking

dlclose(3DL) Close a shared object

dlerror(3DL) Get diagnostic information

dlopen(3DL) Open a shared object

dlsym(3DL) Get the address of a symbol in a shared object


Create a processCreate a process fork, vfork & system: textbook, p162fork, vfork & system: textbook, p162

Notes: Notes:

1. Two generic use for fork: fork & no exec, fork + exec (spawn)1. Two generic use for fork: fork & no exec, fork + exec (spawn)

2. The two main reasons for fork to fail: 2. The two main reasons for fork to fail:

3. Why the child’s PID is returned to the parent process, and a 3. Why the child’s PID is returned to the parent process, and a zero to the child? zero to the child?

4. The child process is a replica of the parent. 4. The child process is a replica of the parent.

5. Copy-on-write(COW) 5. Copy-on-write(COW)

6. The interaction of fork with the I/O functions: stdio functions 6. The interaction of fork with the I/O functions: stdio functions

7. File Sharing 7. File Sharing

8. Inherited properties from the parent process 8. Inherited properties from the parent process

9. Properties Different from the parent process9. Properties Different from the parent process

10. Fork() Safety in the multithreaded environment10. Fork() Safety in the multithreaded environment


Running a programRunning a program

Notes:Notes:

In execlp/execvp, when a filename argument is specified, In execlp/execvp, when a filename argument is specified,

If filename contains a slash, it is taken as a If filename contains a slash, it is taken as a pathname pathname

For execl, execle, and execlp:For execl, execle, and execlp:

char *arg0, char *arg1, …, char *argn, char *arg0, char *arg1, …, char *argn, (char *)(char *)00

the total size of the argument list and the environment : the total size of the argument list and the environment : sysconf( ARG_MAX )sysconf( ARG_MAX )

Use Environ

Try eachPATH prefix

build argvbuild argv

execlp

execvp

execl

execv

build argv

execle

execve


exec() in the kernelexec() in the kernel

kernel code/data/stack

Memory mapped region for shared libraries

runtime heap (via malloc)

program text (.text)

initialized data (.data)

uninitialized data (.bss)

stack

forbidden

0

%espprocess VM

brk

0xc0

physical memorysame

for each process

process-specific datastructures

(page tables,task and mm structs)

kernel VM

To run a new program p in the To run a new program p in the current process using exec():current process using exec():

free vm_area_struct’s and free vm_area_struct’s and page tables for old areas.page tables for old areas.

create new vm_area_struct’s create new vm_area_struct’s and page tables for new areas.and page tables for new areas.

stack, bss, data, text, stack, bss, data, text, shared libs.shared libs.

text and data backed by text and data backed by ELF executable object file.ELF executable object file.

bss and stack initialized to bss and stack initialized to zero.zero.

set PC to entry point in .textset PC to entry point in .text

The kernel will swap in code The kernel will swap in code and data pages as needed.and data pages as needed.

.data.text

p

demand-zero

demand-zero

libc.so

.data.text


Running a programRunning a program

Semantic of the exec familySemantic of the exec family

File descriptors open in the calling process image: close-on-exec File descriptors open in the calling process image: close-on-exec

Directory streams open in the calling process imageDirectory streams open in the calling process image

Signals set to the default action (SIG_DFL) Signals set to the default action (SIG_DFL)

Signals set to be caught by the calling process image: SIG_DFLSignals set to be caught by the calling process image: SIG_DFL

Signals set to be ignored (SIG_IGN) by the calling process image Signals set to be ignored (SIG_IGN) by the calling process image

In a shell which does not support job control, run “In a shell which does not support job control, run “cc xxx &cc xxx &””

any functions previously registered by any functions previously registered by atexit()atexit()

If the set-user-ID mode bit of the new process imageIf the set-user-ID mode bit of the new process image

Any shared memory segments attached to the calling process Any shared memory segments attached to the calling process image image


Terminate a process (1)Terminate a process (1)

Ways for a process to terminate: Ways for a process to terminate:

Normal termination & Abnormal terminationNormal termination & Abnormal termination

Notify its parent how it terminatedNotify its parent how it terminated

Exit status & termination statusExit status & termination status

signal SIGCHLD: SA_NOCLDWAIT set by signactionsignal SIGCHLD: SA_NOCLDWAIT set by signaction

““zombie”: zombie”:

What happened if the parent terminates before the child? What happened if the parent terminates before the child?

Explanations for exit(): atexit() and tmpfile()Explanations for exit(): atexit() and tmpfile()


Terminate a process (2)Terminate a process (2)53 /* 54 * Exit, flushing stdio buffers if necessary. 55 */ 56 void 57 exit( status ) 58 int status; 59 { 60 register struct atexit *p; 61 register int n; 62 63 #ifdef _THREAD_SAFE 64 extern int _thread_autoinit_dummy_decl; 65 /* Ensure that the auto-initialization routine is linked in: */ 66 _thread_autoinit_dummy_decl = 1; 67 #endif 68 69 for (p = __atexit; p; p = p->next) 70 for (n = p->ind; --n >= 0;) 71 (*p->fns[n])(); 72 if (__cleanup) 73 (*__cleanup)(); 74 _exit(status); 75 }


Terminate a process (3)Terminate a process (3) 49 void 50 abort() 51 { 52 sigset_t mask; 53 54 /* 55 * POSIX requires we flush stdio buffers on abort 56 */ 57 if ( __cleanup ) 58 (*__cleanup)(); 59 60 sigfillset( &mask ); 61 /* 62 * don't block SIGABRT to give any handler a chance; we ignore 63 * any errors -- X311J doesn't allow abort to return anyway. 64 */ 65 sigdelset( &mask, SIGABRT ); 66 #ifdef _THREAD_SAFE 67 _thread_sys_sigprocmask(SIG_SETMASK, &mask, (sigset_t *)NULL); 68 #else 69 (void)sigprocmask( SIG_SETMASK, &mask, (sigset_t *)NULL ); 70 #endif 71 (void)kill( getpid(), SIGABRT ); 72 73 exit( 1 ); 74 }


Cleaning up terminated process (1)Cleaning up terminated process (1)Function Description Prototype

wait suspend execution of the calling suspend execution of the calling thread until status information for thread until status information for one of one of its terminated childits terminated child processes is available, or until processes is available, or until delivery of a signaldelivery of a signal whose action whose action is either to execute a signal-is either to execute a signal-catching function or to terminate catching function or to terminate the process the process

pid_t wait( int * stat );

waitpid pid_t waitpid( pid_t pid, int * stat, int options );

waitid (x) suspends the calling process until suspends the calling process until one of its child processes one of its child processes changes changes statestate. It records the current state . It records the current state of a child in the structure pointed of a child in the structure pointed to by infop. to by infop.

int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);

wait3 Wait3() and wait4() allow the Wait3() and wait4() allow the kernel to return a summary kernel to return a summary of the resources used by the of the resources used by the terminated process and all terminated process and all its child processes.its child processes.

pid_t wait3(int *status, int pid_t wait3(int *status, int options, struct rusage options, struct rusage *rusage);*rusage);

wait4 pid_t wait4(pid_t pid, int pid_t wait4(pid_t pid, int *status, int options, struct *status, int options, struct rusage *rusage);rusage *rusage);


Cleaning up terminated process (2)Cleaning up terminated process (2)Constant Description

WNOHANG

WUNTRACED Job control, stopped child processes

Pid’s value

Pid == -1

Pid > 0

Pid == 0

Pid < -1

Macro

WIFEXITED( status ) WEXITSTATUS( status )

WIFSIGNALED( status ) WTERMSIG( status )

WIFSTOPPED( status ) WSTOPSIG( status )


Cleaning up terminated process (3)Cleaning up terminated process (3)

#define WIFEXITED(stat) ((int)((stat)&0xFF) == 0)#define WIFSIGNALED(stat) ((int)((stat)&0xFF) > 0 && \ (int)((stat)&0xFF00) == 0)#define WIFSTOPPED(stat) ((int)((stat)&0xFF) == 0177 && \ (int)((stat)&0xFF00) != 0)

#define WEXITSTATUS(stat) ((int)(((stat)>>8)&0xFF))#define WTERMSIG(stat) ((int)((stat)&0x7F))#define WSTOPSIG(stat) ((int)(((stat)>>8)&0xFF))

The waitpid() function provides three features that are not The waitpid() function provides three features that are not provided by the wait function: provided by the wait function:

waitpid() lets us wait for one particular process (whereas wait() waitpid() lets us wait for one particular process (whereas wait() returns the status of any terminated child). returns the status of any terminated child).

waitpid() provides a nonblocking version of wait(). There are waitpid() provides a nonblocking version of wait(). There are times where we want to fetch a child’s status, but we don’t want times where we want to fetch a child’s status, but we don’t want to block. For example, receiving the signal SIGCHLD. to block. For example, receiving the signal SIGCHLD.

waitpid() supports job control(with the WUNTRACED option). waitpid() supports job control(with the WUNTRACED option).


Cleaning up terminated process (4)Cleaning up terminated process (4)/* the init process */handle( sig_t handler, ... ){ int sig; struct sigaction sa; sigset_t mask_everything; va_list ap;

va_start( ap, handler );

sa.sa_handler = handler; sigfillset( &mask_everything );

while ( ( sig = va_arg(ap, int ) ) != NULL ) { sa.sa_mask = mask_everything; /* XXX SA_RESTART? */ sa.sa_flags = sig == SIGCHLD ? SA_NOCLDSTOP : 0; sigaction( sig, &sa, (struct sigaction *) 0 ); }

va_end( ap );}


Signal OverviewSignal Overview

Unix are designed around a Unix are designed around a virtual-machine modelvirtual-machine model, in , in which system calls are considered to be the parallel of which system calls are considered to be the parallel of machines’ hardware instruction set. machines’ hardware instruction set. Signals are the Signals are the software equivalent of traps or interruptsoftware equivalent of traps or interrupt, a signal-, a signal-handling routine perform the equivalent function of handling routine perform the equivalent function of interrupt or trap service routines. interrupt or trap service routines.

How does the hardware interrupt work? How does the hardware interrupt work?

Interruption source -> 8259 controller->cpu->interrupt vector Interruption source -> 8259 controller->cpu->interrupt vector table->interrupt service routinestable->interrupt service routines

How to write a interrupt handler? How to write a interrupt handler?

Save the context, set the interrupt maskSave the context, set the interrupt mask

May change another stackMay change another stack



=> signal generation, => signal generation,

The kernel is the interrupt controller, The kernel is the interrupt controller,

The destination process is the CPU: mask register, handler vector, etcThe destination process is the CPU: mask register, handler vector, etc

Hardware machine Software virtual machine

Instruction set Set of system calls

Restartable instructions Restartable system calls

Interrupts/traps Signals

Interrupt/trap handlers Signal handlers

Blocking interrupts Masking signals

Interrupt stack Signal stack

DMA Operations Asynchronous I/O operations



Signal GenerationSignal Generation

ExceptionsExceptions

Other processes: sigsend()Other processes: sigsend()

Terminal interrupts: CTRL+cTerminal interrupts: CTRL+c

Job control: stop and continue, notify their parent processJob control: stop and continue, notify their parent process

QuotasQuotas

Notifications: aioNotifications: aio

Alarms: setitimer(), generated by the callout threadAlarms: setitimer(), generated by the callout thread

Actions for signalActions for signal

Default, IGN, Specific HandlerDefault, IGN, Specific Handler


Signal overviewSignal overview

How does the kernel send a signal to the destination How does the kernel send a signal to the destination process?process?

1. get the signal number and the process control block1. get the signal number and the process control block

2. check PCB’s signal block mask, and ignored mask2. check PCB’s signal block mask, and ignored mask

3. if PCB blocked this signal, then pending3. if PCB blocked this signal, then pending

4. if PCB ignored this signal, then discarded now. 4. if PCB ignored this signal, then discarded now.

*** in Solaris, semantics of SIGCHLD*** in Solaris, semantics of SIGCHLD

5. if PCB has a signal hander installed for this signal 5. if PCB has a signal hander installed for this signal

What is the destination process doing now? What is the destination process doing now?

If sleeping for a system call, then wakeup it now. If sleeping for a system call, then wakeup it now.

Put the signal into the process’ signal-q. Put the signal into the process’ signal-q.



Signal handling: Signal handling:

only be taken by the receiving process itself, so only be taken by the receiving process itself, so the process must the process must be scheduled to run. be scheduled to run.

The receiving process becomes aware of the signal when the The receiving process becomes aware of the signal when the kernel does check for pending signal. The kernel checks at the kernel does check for pending signal. The kernel checks at the following times: following times:

Before returning to user mode Before returning to user mode from a system call or interruptfrom a system call or interrupt. .

Just before blocking on an interruptible event. Just before blocking on an interruptible event.

Immediately after waking up from an interruptible event.Immediately after waking up from an interruptible event.

How does the kernel prepare the context for the signal handler? How does the kernel prepare the context for the signal handler?

Stack frame: signum, siginfo_t, ucontext *, and a instruction Stack frame: signum, siginfo_t, ucontext *, and a instruction which will re-enter the kernel againwhich will re-enter the kernel again

Nested signal handling??? Very Difficult. Nested signal handling??? Very Difficult.



Conclusions:Conclusions:

Signals generated by asynchronous events may occur after Signals generated by asynchronous events may occur after any any instructioninstruction in the code path of the process. in the code path of the process.

We need mechanisms to block the specific signals during We need mechanisms to block the specific signals during running. The most progress in O.S. designrunning. The most progress in O.S. design

Book, p6-7Book, p6-7

In multithreaded program, signal handling becomes rather In multithreaded program, signal handling becomes rather difficult there. difficult there.

In Solaris’s implementation, signal handling is difficult too. In Solaris’s implementation, signal handling is difficult too.

Generation -> notification -> redirect -> delivered Generation -> notification -> redirect -> delivered

There is a LWP to wait for signals, and then dispatch to a There is a LWP to wait for signals, and then dispatch to a thread. thread.


Signal Handling in LinuxSignal Handling in Linux


History about signal handlingHistory about signal handling unreliable signal: See two classical code: race conditionunreliable signal: See two classical code: race condition

example 1: int sig_int(); /* singal hander */ int main( int argc, char **argv ){ ... signal( SIGINT, sig_int ); /* install my own signal handler */ ....}

voidsig_int( int signum ){ /* here the kernel sends a signal again, I don’t get it here.. */

signal( SIGINT, sig_int ); /* reinstall the signal handler */ }


History about signal handlingHistory about signal handlingExample 2:static volatile sig_atomic_t sig_int_flag; /* set nonzero when signal occurs */

intmain( int argc, char **argv ){ int sig_int(); signal( SIGINT, sig_int ); while ( sig_int_flag == 0 ) /* I may lose the signal here */ pause(); /* waiting for a incoming signal */ ...}

void sig_int( int signum ){ signal( SIGINT, sig_int ); sig_int_flag = 1;}


History about signal handlingHistory about signal handling

Reliable signal handlingReliable signal handling

1. permanent signal handling1. permanent signal handling

2. masking to protect the critical area: masked = blocked2. masking to protect the critical area: masked = blocked

3. atomic unblocked and waiting operation: sigsuspend()3. atomic unblocked and waiting operation: sigsuspend()

4. for performance, put signal masks into PCB, so we need not 4. for performance, put signal masks into PCB, so we need not wakeup some process nowwakeup some process now


Issues about signal handlingIssues about signal handling

Restartable system callsRestartable system calls

Waiting for a device operation of slow speed: socket, terminalWaiting for a device operation of slow speed: socket, terminal

errno == EINTRerrno == EINTR

Reentrant functionsReentrant functions

Called by both the main program and signal handlerCalled by both the main program and signal handler

stdio, malloc/free, routines using global variablesstdio, malloc/free, routines using global variables

I/O operations with timeoutI/O operations with timeout

Use longjmp() & setjmp(), but Use longjmp() & setjmp(), but signal interactionsignal interaction

Use select()/poll()Use select()/poll()

There is no other good means for this requirements now.There is no other good means for this requirements now.


Functions about signal (1)Functions about signal (1)

1. sending signals1. sending signals

kill( pid_t pid, int sig ): pid, see waitpid()kill( pid_t pid, int sig ): pid, see waitpid()

sigsend( idtype_t, id_t, int ): idtype_t, see waitid()sigsend( idtype_t, id_t, int ): idtype_t, see waitid()

2. using signal sets2. using signal sets

sigset_t: p6-11sigset_t: p6-11

sigprocmask(): p6-12, 13, operating the process’ blocked masksigprocmask(): p6-12, 13, operating the process’ blocked mask

Remember: restore the old mask: SIG_SETMASKRemember: restore the old mask: SIG_SETMASK

Catching signals: p6-15, 16, 17, 18, Catching signals: p6-15, 16, 17, 18,

void ( *signal( int signum, void (*sighandler)(int) ) )(int);void ( *signal( int signum, void (*sighandler)(int) ) )(int);

Using sigaction() is the best choice. Using sigaction() is the best choice.

Flag SA_SIGINFOFlag SA_SIGINFO

See the examples sigaction.c: use workshop to evaluate siginfo_t See the examples sigaction.c: use workshop to evaluate siginfo_t



Catching SIGCHLDCatching SIGCHLD

1. in the main program, invoke wait()/waitpid()1. in the main program, invoke wait()/waitpid()

2. install a SIGCHLD handler, and in which we should use wait2. install a SIGCHLD handler, and in which we should use wait

3. ignore SIGCHLD3. ignore SIGCHLD

4. use sigaction() and the flag SA_NOCLDWAIT4. use sigaction() and the flag SA_NOCLDWAIT

5. fork() and fork(): ask the init process reap my sons5. fork() and fork(): ask the init process reap my sons


Example - SIGCHLDExample - SIGCHLD1.1. void childhandler( int signo ) void childhandler( int signo )

2.2. {{

… …

3.3. saveerrno = errno;saveerrno = errno;

4.4. /* get all outstanding terminated children *//* get all outstanding terminated children */

5.5. for ( ;; ) for ( ;; )

6.6. { {

7.7. pid = waitpid( -1, &status, WNOHANG );pid = waitpid( -1, &status, WNOHANG );

8.8. if ( pid == 0 ) {if ( pid == 0 ) {

9.9. /* 1. no dead children, but some live ones *//* 1. no dead children, but some live ones */

10.10. break;break;

11.11. } else if ( pid == -1 && errno == ECHILD ) {} else if ( pid == -1 && errno == ECHILD ) {

12.12. /* 2. no more children, dead or running *//* 2. no more children, dead or running */

13.13. break;break;

14.14. } else if (pid == -1) {} else if (pid == -1) {

15.15. /* should not get this *//* should not get this */

16.16. perror("waitpid");perror("waitpid");

17.17. abort();abort();

18.18. }}

19.19. /* 3. status contains the reaped status of one child *//* 3. status contains the reaped status of one child */

20.20. /* If desired, save status for main program. *//* If desired, save status for main program. */

21.21. }}

22.22. errno = saveerrno;errno = saveerrno;

23.23. return;return;

24.24. }} // // sig_atomic_t sig_atomic_t



Using alarm signalsUsing alarm signals

alarm(), Textbook, p167: timeout.calarm(), Textbook, p167: timeout.c

setitimer() & getitimer():setitimer() & getitimer():

setitimer(): itimerval.it-value, current value?setitimer(): itimerval.it-value, current value?

!!!! Read man setitimer carefully, specially used in the !!!! Read man setitimer carefully, specially used in the multithreaded environmentmultithreaded environment

Notes: Notes:

Timer set by setitimer() is permanent. Timer set by setitimer() is permanent.

There is only 4 timers for one process. So we need implement our own There is only 4 timers for one process. So we need implement our own software timeout mechanism sometime. software timeout mechanism sometime.

Hint: Data-link timer queue management Hint: Data-link timer queue management

sigsetjmp() & siglongjmp() & timeout => timed system callsigsetjmp() & siglongjmp() & timeout => timed system call



Waiting for a signal:Waiting for a signal:

sigpause( int signum ); a particular signalsigpause( int signum ); a particular signal

Used in the synchronization between parent & child processesUsed in the synchronization between parent & child processes

sigsuspend( sigset_t *set ); /****** important *******/sigsuspend( sigset_t *set ); /****** important *******/

Atomic unblock and waiting: reliable signalAtomic unblock and waiting: reliable signal

Example: Example:

sigprocmask( SIG_BLOCK, &newset, &oldmask );sigprocmask( SIG_BLOCK, &newset, &oldmask );

/* critical region *//* critical region */

if ( condition ) /* may while ( flag ), */if ( condition ) /* may while ( flag ), */

sigsuspend( &set );sigsuspend( &set );

sigprocmask( SIG_SETMASK, &oldmask, NULL );sigprocmask( SIG_SETMASK, &oldmask, NULL );

Remember: during waiting for a signal, and at the Remember: during waiting for a signal, and at the same time invoking a system call, same time invoking a system call, no reliable waysno reliable ways now.now.


ExerciseExercise

1. Notes: 1. Notes:

The child process's tms structure is cleared: tms_utime , stime , The child process's tms structure is cleared: tms_utime , stime , cutime , and cstime are set to 0 (using cutime , and cstime are set to 0 (using times(2)times(2)).).

The child processes resource utilizations are set to 0. The The child processes resource utilizations are set to 0. The it_value and it_interval values for the ITIMER_REAL timer are it_value and it_interval values for the ITIMER_REAL timer are reset to 0.reset to 0.

The set of signals pending for the child process is initialized to The set of signals pending for the child process is initialized to the empty set.the empty set.

Suggestions:Suggestions:

Take into more and more careful consideration: interactions Take into more and more careful consideration: interactions

Use the traditional ways to handle signalUse the traditional ways to handle signal

Separate the signal handling/critical region from the remainderSeparate the signal handling/critical region from the remainder


Process Relationship (1)Process Relationship (1)

Controlling Terminal

Process Group

Current

Session

foreground

Background

Process

Parent1

1..n

+BelongTo

1

1..n

Leader

UserGroup

User

euid

11

Supplementary

ruid

saved_euid


Process Relationship (3)Process Relationship (3)

Session

Background Process GroupSession Leader = Controlling

Process Background Process Group

Foreground Process Group

ControllingTerminal

Han

gup

Sig

nal

Terminal In

put and terminal-generated signals

History: System V & BSD => Session( job control, login )History: System V & BSD => Session( job control, login )

The init processThe init process


System and Process InformationSystem and Process Information

Host information: Book, p3-4,Host information: Book, p3-4,

System variablesSystem variables

File and directory limitsFile and directory limits

Machine timeMachine time

Converting timeConverting time

Time usage Time usage

unix system interface programming part 6.3 – process and signal prepared by xu zhenya(...

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