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Full Discussion: C Brain Teaser
Top Forums Programming C Brain Teaser Post 302116922 by Perderabo on Wednesday 9th of May 2007 09:22:19 AM
Old 05-09-2007
Astounding that that works, vino! Looking at the Linux man page for unlink(2), I see that it does not detect "text busy". Compare that to the HP-UX man page for unlink(2). The Linux unlink(2) is rather permissive. If that man page is right, it even allows unlinking an active mount point! I'm not sure what effect that would have... Posix does not require that unlink(2) disallow unlinking mount points (but the text in the standard makes it clear that this is because Posix does not ever mention mount points). But unlinking an active program is another matter. On one hand, the Posix Standard says:
Quote:
The unlink() function shall fail and shall not unlink the file if:
...
[ETXTBSY] The entry to be unlinked is the last link to a pure procedure (shared text) file that is being executed.
That sounds to me like an OS is required to disallow the operation. But toward the end of the page we have:
Quote:
The [ETXTBSY] optional error condition is added.
This leaves me confused as to whether or not the operation is allowed by Posix. But it will not work on most implementations of Unix. I would be interested if this program works with any kernel other than Linux.

A more portable solution would be have the program to write a little shell script to unlink the file and then exec that shell script.
 

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link(1) 						      General Commands Manual							   link(1)

NAME
link, unlink - Creates an additional directory entry for an existing file SYNOPSIS
link file1 file2 unlink file STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: link: XCU5.0 unlink: XCU5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. DESCRIPTION
The link command performs the link() system call to create an additional directory entry for an existing file, file1. In effect, the underlying file then has two names, file1 and file2 (either of these arguments can be a pathname). The old and new entries share equal access rights to the underlying file. The unlink command performs the unlink() system call to remove a link to file created by link. The unlink command removes the directory entry specified by the file parameter and, if the entry is a hard link, decrements the link count of the file referenced by the link. You should be familiar with the link() and unlink() system calls before you use these commands. The link and unlink commands do not issue error messages when the associated system call is unsuccessful. NOTES
The link and unlink commands cannot be used to link and unlink directories. EXIT STATUS
The link and unlink commands both exit with the following: The link() or unlink() system call succeeded. Too few or too many arguments specified. The link() or unlink() system call failed. SEE ALSO
Commands: fsck(8), ln(1) Functions: link(2), unlink(2) link(1)
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