Home » Birth is empty on ext4

Birth is empty on ext4

Solutons:


The field gets populated (see below) only coreutils stat does not display it. Apparently they’re waiting1 for the xstat() interface.

coreutils patches – aug. 2012 – TODO

stat(1) and ls(1) support for birth time. Dependent on xstat() being
provided by the kernel

You can get the creation time via debugfs:

debugfs -R 'stat <inode_number>' DEVICE

e.g. for my /etc/profile which is on /dev/sda2 (see How to find out what device a file is on):

stat -c %i /etc/profile
398264
debugfs -R 'stat <398264>' /dev/sda2
debugfs 1.42.5 (29-Jul-2012)
Inode: 398264   Type: regular    Mode:  0644   Flags: 0x80000
Generation: 2058737571    Version: 0x00000000:00000001
User:     0   Group:     0   Size: 562
File ACL: 0    Directory ACL: 0
Links: 1   Blockcount: 8
Fragment:  Address: 0    Number: 0    Size: 0
 ctime: 0x506b860b:19fa3c34 -- Wed Oct  3 02:25:47 2012
 atime: 0x50476677:dcd84978 -- Wed Sep  5 16:49:27 2012
 mtime: 0x506b860b:19fa3c34 -- Wed Oct  3 02:25:47 2012
crtime: 0x50476677:dcd84978 -- Wed Sep  5 16:49:27 2012
Size of extra inode fields: 28
EXTENTS:
(0):3308774

Time fields meaning:

  • ctime: file change time.
  • atime: file access time.
  • mtime: file modification time.
  • crtime: file creation time.

1 Linus’ reply on LKML thread

I combined this into a simple shell function:

get_crtime() {
  for target in "${@}"; do
    inode=$(stat -c %i "${target}")
    fs=$(df  --output=source "${target}"  | tail -1)
    crtime=$(sudo debugfs -R 'stat <'"${inode}"'>' "${fs}" 2>/dev/null | 
    grep -oP 'crtime.*--s*K.*')
    printf "%st%sn" "${target}" "${crtime}"
  done
    }

You can then run it with

$ get_crtime foo foo/file /etc/
foo Wed May 21 17:11:08 2014
foo/file    Wed May 21 17:11:27 2014
/etc/   Wed Aug  1 20:42:03 2012

The xstat function never got merged into mainline. However, a new statx call was proposed later on, and was merged in Linux 4.11. The new statx(2) system call does include a creation time in its return struct. A wrapper for statx(2) was added to glibc only in 2.28 (release August 2018). And support for using this wrapper was added in GNU coreutils 8.31 (released March 2019):

stat now prints file creation time when supported by the file system,
on GNU Linux systems with glibc >= 2.28 and kernel >= 4.11.

% stat --version
stat (GNU coreutils) 8.31
Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Michael Meskes.
% stat /
  File: /
  Size: 4096            Blocks: 8          IO Block: 4096   directory
Device: b302h/45826d    Inode: 2           Links: 17
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-06-06 20:03:12.898725626 +0900
Modify: 2019-05-28 05:15:44.452651395 +0900
Change: 2019-05-28 05:15:44.452651395 +0900
 Birth: 2018-06-07 20:35:54.000000000 +0900

What follows is a demo of statx where userland has yet to catch up (older glibc or coreutils). It’s not easy to call system calls directly in a C program. Typically glibc provides a wrapper that makes the job easy, but Luckily, @whotwagner wrote a sample C program that shows how to use the statx(2) system call on x86 and x86-64 systems. Its output is the same format as stat‘s default, without any formatting options, but it’s simple to modify it to print just the birth time. (If you have a new enough glibc, you won’t need this – you can use statx directly as described in man 2 statx).

First, clone it:

git clone https://github.com/whotwagner/statx-fun

You can compile the statx.c code, or, if you just want the birth time, create a birth.c in the cloned directory with the following code (which is a minimal version of statx.c printing just the creation timestamp including nanosecond precision):

#define _GNU_SOURCE
#define _ATFILE_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include "statx.h"
#include <time.h>
#include <getopt.h>
#include <string.h>

// does not (yet) provide a wrapper for the statx() system call
#include <sys/syscall.h>

/* this code works ony with x86 and x86_64 */
#if __x86_64__
#define __NR_statx 332
#else
#define __NR_statx 383
#endif

#define statx(a,b,c,d,e) syscall(__NR_statx,(a),(b),(c),(d),(e))

int main(int argc, char *argv[])
{
    int dirfd = AT_FDCWD;
    int flags = AT_SYMLINK_NOFOLLOW;
    unsigned int mask = STATX_ALL;
    struct statx stxbuf;
    long ret = 0;

    int opt = 0;

    while(( opt = getopt(argc, argv, "alfd")) != -1)
    {
        switch(opt) {
            case 'a':
                flags |= AT_NO_AUTOMOUNT;
                break;
            case 'l':
                flags &= ~AT_SYMLINK_NOFOLLOW;
                break;
            case 'f':
                flags &= ~AT_STATX_SYNC_TYPE;
                flags |= AT_STATX_FORCE_SYNC;
                break;
            case 'd':
                flags &= ~AT_STATX_SYNC_TYPE;
                flags |= AT_STATX_DONT_SYNC;
                break;
            default:
                exit(EXIT_SUCCESS);
                break;
        }
    }

    if (optind >= argc) {
        exit(EXIT_FAILURE);
    }

    for (; optind < argc; optind++) {
        memset(&stxbuf, 0xbf, sizeof(stxbuf));
        ret = statx(dirfd, argv[optind], flags, mask, &stxbuf);
        if( ret < 0)
        {
            perror("statx");
            return EXIT_FAILURE;
        }
        printf("%lld.%un", *&stxbuf.stx_btime.tv_sec, *&stxbuf.stx_btime.tv_nsec);
    }
    return EXIT_SUCCESS;
}

Then:

$ make birth
$ ./birth ./birth.c
1511793291.254337149
$ ./birth ./birth.c | xargs -I {} date -d @{}
Mon Nov 27 14:34:51 UTC 2017

In theory this should make the creation time accessible on more filesystems than just the ext* ones (debugfs is a tool for ext2/3/4 filesystems, and unusable on others). It did work for an XFS system, but not for NTFS and exfat. I guess the FUSE filesystems for those didn’t include the creation time.

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