CODEWITHSUNDEEP
cpermissionsfile-ownership
Chris
Chris

Reputation: 2060

Keeping fileowner and permissions after copying file in C

here is my problem: In C, I create the copy of a file (with some changes) This is done trivially via fopen(), getchar and putchar. Copying the file is fine and the outputfile itself is what I want it to be.

My problem is: I assume that I will use this program often as sudo and then the resulting file has both another owner (root) as well as different permissions (execute rights are gone).

My question is: How can I copy the owner and permissions of the original file and then write them into the new one?

Upvotes: 0

Views: 4022

Answers (3)

user237419
user237419

Reputation: 9064

since you use fopen():

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

//fp is your source filepointer, fdest is your dest filepointer
//fn is the  new filename you're copying to

struct stat fst;
//let's say this wont fail since you already worked OK on that fp
fstat(fileno(fp),&fst);
//update to the same uid/gid
fchown(fileno(fdest),fst.st_uid,fst.st_gid);
//update the permissions 
fchmod(fileno(fdest),fst.st_mode);

as a quick note, you may want to fread() and fwrite() instead of f*char()'ing

Upvotes: 2

Diomidis Spinellis
Diomidis Spinellis

Reputation: 19345

Use the fstat(2) system call to obtain the details about the owner and the permissions, and the fchmod(2) and fchown(2) system calls to set them. See an example in the setfile function of the *BSD cp(1) source code.

Upvotes: 2

Angelom
Angelom

Reputation: 2531

Under linux use the libc fchmod and fchown Manpages can be found here:

http://linux.die.net/man/2/fchmod

http://linux.die.net/man/2/fchown

Upvotes: 0

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