03-28-2009
The arguments absolutely must be separated because each argument will be a separate element in the argv array. Things like shells and the system() subroutine accept arguments separated by spaces, but they must isolate each argument prior to calling exec().
exec() tells the kernel to replace the current existing program with a new program. The kernel roughly:
1. saves a copy of the new argv array and a copy of the environment
2. frees any private memory area
3. disconnects the process from any shared memory area including a shared text segment and any shared libraries.
Note: At this point, any code following the exec call no longer exists in the process. The same is true of any code prior to the exec call and even the exec call itself. It's all gone.
4. reads in the exec'ed program and reconstructs a working program. The environment and the arguments are copied into the new program.
5. transfers control to the newly created program.
Note that this all happens in one process. The process id does not change. The program that the process is running changes. After an exec() a process might be smaller (use less memory) than it did prior to the exec().
You can't emulate stuff like this in userland. Only the kernel can do this sort of thing.
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LEARN ABOUT DEBIAN
ns_execargv
Ns_Exec(3aolserver) AOLserver Library Procedures Ns_Exec(3aolserver)
__________________________________________________________________________________________________________________________________________________
NAME
Ns_ExecArgblk, Ns_ExecArgv, Ns_ExecProc, Ns_ExecProcess, Ns_Fork, Ns_GetEnviron, Ns_WaitForProcess, Ns_WaitProcess, ns_fork - External
process execution
SYNOPSIS
#include "ns.h"
int
Ns_ExecArgblk(char *exec, char *dir, int fdin, int fdout,
char *args, Ns_Set *env)
int
Ns_ExecArgv(char *exec, char *dir, int fdin, int fdout,
char **argv, Ns_Set *env)
int
Ns_ExecProc(char *exec, char **argv)
int
Ns_ExecProcess(char *exec, char *dir, int fdin, int fdout,
char *args, Ns_Set *env)
int
Ns_Fork(void)
char
**Ns_GetEnviron(void)
int
Ns_WaitForProcess(int pid, int *statusPtr)
int
Ns_WaitProcess(int pid)
int
ns_fork(void)
_________________________________________________________________
DESCRIPTION
These functions handle fork and exec operations. See files: nsd/exec.c, nsd/tclenv.c and nsthread/fork.c.
Ns_ExecArgblk(exec, dir, fdin, fdout, args, env)
Executes a command in a child process. Return process id of child process exec'ing the command or -1 on failure. Provides extended
error checking and error messages.
Ns_ExecArgv(exec, dir, fdin, fdout, argv, env)
Execute a command in a child process using fork(2) and execve(2), returns the process id of child process exec'ing the command or -1
on failure. The child sends an extended error message to the parent.
Ns_ExecProc(exec, argv)
Executes a command in a child process. Returns the process id of the child process exec'ing the command or -1 on failure. Simpli-
fies call to Ns_ExecArgv.
Ns_ExecProcess(exec, dir, fdin, fdout, args, env)
Executes a command in a child process. Returns the process id of the child process exec'ing the command or -1 on failure. Calls
Ns_ExecArgblk with same arguments.
Ns_Fork()
Posix style fork(), using fork1() on Solaris if needed. See fork(2) man page. Calls ns_fork.
Ns_GetEnviron()
Returns pointer to the environment vector.
Ns_WaitForProcess(pid, statusPtr)
Wait for child process. Returns NS_OK on success, or NS_ERROR on failure. *statusPtr is set to the exit code of the child process.
Ns_WaitProcess(pid)
Wait for child process. Calls Ns_WaitForProcess with NULL statusPtr. Returns NS_OK on success, or NS_ERROR on failure.
ns_fork()
Posix style fork(), using fork1() on Solaris if needed.
SEE ALSO
nsd(1), info(n)
KEYWORDS
AOLserver 4.0 Ns_Exec(3aolserver)