I understand that a directory is just a file in unix that contains the inode numbers and names of the files within. How do I take a look at this? I can't use cat or less on a directory, and opening it in vi just shows me a listing of the files...no inode numbers.
+1
A:
It looks like the stat command might be in order. From the article:
stat /etc/passwd
File: `/etc/passwd'
Size: 2911 Blocks: 8 IO Block: 4096 regular file
Device: fd00h/64768d Inode: 324438 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2008-08-11 05:24:17.000000000 -0400
Modify: 2008-08-03 05:11:05.000000000 -0400
Change: 2008-08-03 05:11:05.000000000 -0400
Michael Haren
2009-11-02 01:46:36
The stat command gives basic info about the file or directory, but it doesn't tell me anything about the files inside. For example, using "stat" on the directory pointed to by /etc gives me:234881026 2995 drwxr-xr-x 91 root wheel 0 3094 "Oct 29 11:27:39 2009" "Sep 26 23:09:45 2009" "Sep 26 23:09:45 2009" 4096 0 0 /private/etc
Goose Bumper
2009-11-02 01:55:55
statvfs() is the more preferable function to use, in general practice.
Tim Post
2009-11-02 02:18:56
+7
A:
Since this is a programming question (it is a programming question, isn't it?), you should check out the opendir, readdir and closedir functions. These are part of the Single UNIX Spec.
#include <sys/types.h>
#include <dirent.h>
DIR *opendir (const char *dirname);
struct dirent *readdir(DIR *dirp);
int closedir(DIR *dirp);
The dirent.h file should have the structure you need, containing at least:
char d_name[] name of entry
ino_t d_ino file serial number
See here for the readdir manpage - it contains links to the others.
Keep in mind that the amount of information about a file stored in the directory entries for it is minimal. The inode itself contains the stuff you get from the stat function, things like times, size, owner, permissions and so on, along with the all-important pointers to the actual file content.
paxdiablo
2009-11-02 01:59:35
Ah, I see. But is there any way to see the literal, actual contents of the file? Maybe this example will make it clearer: on my setup, I can enter "less /bin/ls" to see the contents of ls. It's not legible in any way, obviously, but I can still see it. Can I do the same for directories in some way?It's not a practical question, it's more that I'm curious whether Unix allows a user to do something like this.
Goose Bumper
2009-11-02 02:55:06
I've never seen a user-level command capable of doing this (that doesn't mean it doesn't exist). However, with a bit of work, you could get the inode of the actual directory you're interested in (from the parent directory) and walk the actual structures on the hard disk, assuming you have the requisite permissions.
paxdiablo
2009-11-02 03:00:52
Perfect, thank you. It looks like there's no easy solution, but a little googling showed that there are some C functions worth investigating.
Goose Bumper
2009-11-02 03:15:53
+3
A:
In the old days - Version 7, System III, early System V - you could indeed open a directory and read the contents into memory, especially for the old Unix file system with 2-byte inode numbers and a limit of 14 bytes on the file name.
As more exotic file systems became more prevalent, the opendir(), readdir(), closedir() family of function calls had to be used instead because parsing the contents of a directory became increasingly non-trivial.
Finally, in the last decade or so, it has reached the point where on most systems, you cannot read the directory; you can open it (primarily so operations such as fchdir() can work), and you can use the opendir() family of calls to read it.
Jonathan Leffler
2009-11-02 02:05:06