CODEWITHSUNDEEP
clinuxtemporary-files
matheuscscp
matheuscscp

Reputation: 878

When a file created with mkstemp() is deleted?

I have a program that calls mkstemp(), writes some stuff with the fd returned and then closes the fd. I want the file to remain until I delete it myself! With something like rm command, or whatever. My question is: will Linux delete this file after close(fd)?

Upvotes: 8

Views: 9078

Answers (3)

mehmet riza oz
mehmet riza oz

Reputation: 559

The Linux Programming Interface book gives best answer to this question. Regard the comments in the code below.

Typically, a temporary file is unlinked (deleted) soon after it is opened, using the unlink() system call (Section 18.3). Thus, we could employ mkstemp() as follows:

int fd;
char template[] = "/tmp/somestringXXXXXX";
fd = mkstemp(template);
if (fd == -1)
    errExit("mkstemp");
    printf("Generated filename was: %s\n", template);
    unlink(template);
    /* Name disappears immediately, but the file
    is removed only after close() */
    /* Use file I/O system calls - read(), write(), and so on */
if (close(fd) == -1)
    errExit("close");

Upvotes: 0

Konrad Rudolph
Konrad Rudolph

Reputation: 546123

will Linux delete this file after close(fd)?

Not automatically. You need to call unlink on the file manually. You can do this immediately after calling mkstemp if you don’t need to access the file by name (i.e. via the file system) — it will then be deleted once the descriptor is closed.

Alternatively, if you need to pass the file on to another part of the code (or process) by name, don’t call unlink just yet.

Here’s an example workflow:

char filename[] = "tempfile-XXXXXX";
int fd;
if ((fd = mkstemp(filename)) == -1) {
    fprintf(stderr, "Failed with error %s\n", strerror(errno));
    return -1;
}

unlink(filename);

FILE *fh = fdopen(fd, "w");
fprintf(fh, "It worked!\n");
fclose(fh);

fclose closes the FILE* stream, but also the underlying file descriptor, so we don’t need to explicitly call close(fd).

Necessary headers:

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

Upvotes: 15

gengisdave
gengisdave

Reputation: 2050

No, when a file is created with tmpfile(), its directory entry (in the temporary directory) is removed after the creation, so there is only the file descriptor referenced by open that leads to the file inodes (in the /proc/<pid>/fd directory); once you call close(fd), there are no more reference to the file.

With mkstemp() you have to do it manually with unlink() right after the creation.

Upvotes: 0

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