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   exec.3p    ( 3 )

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Использование в приложениях (Application usage)

As the state of conversion descriptors and message catalog descriptors in the new process image is undefined, conforming applications should not rely on their use and should close them prior to calling one of the exec functions.

Applications that require other than the default POSIX locale as the global locale in the new process image should call setlocale() with the appropriate parameters.

When assigning a new value to the environ variable, applications should ensure that the environment to which it will point contains at least the following:

1. Any implementation-defined variables required by the implementation to provide a conforming environment. See the _CS_V7_ENV entry in <unistd.h> and confstr() for details.

2. A value for PATH which finds conforming versions of all standard utilities before any other versions.

The same constraint applies to the envp array passed to execle() or execve(), in order to ensure that the new process image is invoked in a conforming environment.

Applications should not execute programs with file descriptor 0 not open for reading or with file descriptor 1 or 2 not open for writing, as this might cause the executed program to misbehave. In order not to pass on these file descriptors to an executed program, applications should not just close them but should reopen them on, for example, /dev/null. Some implementations may reopen them automatically, but applications should not rely on this being done.

If an application wants to perform a checksum test of the file being executed before executing it, the file will need to be opened with read permission to perform the checksum test.

Since execute permission is checked by fexecve(), the file description fd need not have been opened with the O_EXEC flag. However, if the file to be executed denies read and write permission for the process preparing to do the exec, the only way to provide the fd to fexecve() will be to use the O_EXEC flag when opening fd. In this case, the application will not be able to perform a checksum test since it will not be able to read the contents of the file.

Note that when a file descriptor is opened with O_RDONLY, O_RDWR, or O_WRONLY mode, the file descriptor can be used to read, read and write, or write the file, respectively, even if the mode of the file changes after the file was opened. Using the O_EXEC open mode is different; fexecve() will ignore the mode that was used when the file descriptor was opened and the exec will fail if the mode of the file associated with fd does not grant execute permission to the calling process at the time fexecve() is called.