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In what order are the dated ordered by? Certainly not alphanumeric order.

ls -lt sorts by modification time. But I need creation time.

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up vote 43 down vote accepted

Most unices do not have a concept of file creation time. You can't make ls print it because the information is not recorded. If you need creation time, use a version control system: define creation time as the check-in time.

If your unix variant has a creation time, look at its documentation. For example, on Mac OS X (the only example I know of¹), use ls -tU. Windows also stores a creation time, but it's not always exposed to ports of unix utilities, for example Cygwin ls doesn't have an option to show it. The stat utility can show the creation time, called “birth time” in GNU utilities, so under Cygwin you can show files sorted by birth time with stat -c '%W %n' * | sort -k1n.

Note that the ctime (ls -lc) is not the file creation time, it's the inode change time. The inode change time is updated whenever anything about the file changes (contents or metadata) except that the ctime isn't updated when the file is merely read (even if the atime is updated). In particular, the ctime is always more recent than the mtime (file content modification time) unless the mtime has been explicitly set to a date in the future.

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In Cygwin it is ls -c. ls --help shows what -c does when combined with -l and -lt. – Aaron D. Marasco Sep 12 '11 at 1:37
@Aaron No, the ctime is not the creation time. It's a common confusion based purely on the fact that “ctime” and “creation” start with the same letter, but there is no relation between ctime and creation time. I've updated my answer to address this confusion. – Gilles Sep 12 '11 at 11:31
LOL my bad. I was trying to confirm the Cygwin part for ya (IIRC your original post had a possible command). It does specifically say "ctime (time of last modification of file status information)" if I had paid attention. – Aaron D. Marasco Sep 13 '11 at 2:02
Adding to @Gilles answer; I use an NFS 3.x file server (unsure on the underlying file system; it's either UFS or ZFS, though I'm guessing UFS). Under Redhat 6.x: -U sorts by creation time. Under Solaris 10.x: /usr/bin/ls does not support -U, /usr/ucb/ls supports -U and does sort by creation time. These results obviously depend on the filesystem storing that info in the first place. – Brian Vandenberg Jun 12 '12 at 19:44
@ghoti If no files were ever deleted (or moved/renamed/hardlinked/…) in the directory, then the directory order is creation order on some filesystems, but not all. That's not true on ext4, for example. I don't know if it's true on Solaris's UFS. – Gilles yesterday

Unfortunately, the stat(2) API does not provide a way to get the file creation time, as it is not required by the Unix standards.

However, some filesystems, as ext4, do save this information within the file metadatas. There is just no standard way to get it, but there is a way (ext filesystems only):

debugfs -R 'stat partition/relative/path/to/file' /dev/sda1

You would get something like that mentioning crtime (not ctime!) if you use ext4.

 ctime: 0x513a50e5:d4e448f0 -- Fri Mar  8 21:58:13 2013
 atime: 0x513dd8f1:04df0b20 -- Mon Mar 11 14:15:29 2013
 mtime: 0x513a50e5:d4e448f0 -- Fri Mar  8 21:58:13 2013
crtime: 0x513a259a:35191a3c -- Fri Mar  8 18:53:30 2013

This command may take some time to return, probably because it also lists every extent related to the file.

Now if you want to order files by creation date, I guess this is not easily (nor properly) possible. As Gilles says, it would probably be easier if you'd use a revision control system. But you may try to have a look at the ext4 API...

I tried the stat -c '%w' myfile command on a ext4 filesytem on a (recent enough) Ubuntu system without success (it just answers -).

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