$ git ls-tree fb3a8bdd0ce
100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c    .gitignore
100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d    .mailmap
100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3    COPYING
040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745    Documentation
100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200    GIT-VERSION-GEN
100644 blob 289b046a443c0647624607d471289b2c7dcd470b    INSTALL
100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1    Makefile
100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52    README

I know the last 3 oct digits are file mode, but what are the first 3 digits for? I can't find it out in git user's manual.


From the Git index-format.txt file, regarding the mode:

32-bit mode, split into (high to low bits)

    4-bit object type
      valid values in binary are 1000 (regular file), 1010 (symbolic link)
      and 1110 (gitlink)

    3-bit unused

    9-bit unix permission. Only 0755 and 0644 are valid for regular files.
    Symbolic links and gitlinks have value 0 in this field.

Also, a directory object type (binary 0100) and group-writeable (0664 permissions) regular file are allowed as indicated by the fsck.c fsck_tree method. The regular non-executable group-writeable file is a non-standard mode that was supported in earlier versions of Git.

This makes valid modes (as binary and octal):

  • 0100000000000000 (040000): Directory
  • 1000000110100100 (100644): Regular non-executable file
  • 1000000110110100 (100664): Regular non-executable group-writeable file
  • 1000000111101101 (100755): Regular executable file
  • 1010000000000000 (120000): Symbolic link
  • 1110000000000000 (160000): Gitlink
  • 2
    The directory mode is not valid because it will never happen. Git doesn't track directories, because directories in Git exist only implicitly with un-ignored content.
    – nemesis
    Mar 24 '14 at 16:21
  • 2
    @nemesis Git indeed uses the directory (040000) mode to represent directories. Please see the linked fsck.c code, or just execute git ls-tree HEAD in a Git repository that contains directories.
    – Dan Cruz
    Mar 24 '14 at 17:53
  • 3
    @CiroSantilli巴拿馬文件六四事件法轮功: group write permission isn't actually kept. It's just that the fsck code won't claim that a tree entry with that mode is bad. The idea was to leave room for group permissions on files, if it turned out to be needed. It was never needed, hence never added, but the testing code was never changed to forbid it either.
    – torek
    Jul 23 '16 at 0:16
  • 2
    @Dan Cruz If there are only 16 base-2 digits, why they write 32-bit mode? Aug 21 '18 at 4:25
  • 2
    @Sevastyan Git reserves 16 bits for internal usage; see cache.h.
    – Dan Cruz
    Aug 21 '18 at 18:10

The 6 digits show the file mode using the classical UNIX notations. First two digits show file type, the third one is about set-uid/set-gid/sticky bits, and you know the last three.

Here is how man 2 stat documents it on my GNU/Linux system:

   The following flags are defined for the st_mode field:

       S_IFMT     0170000   bit mask for the file type bit fields
       S_IFSOCK   0140000   socket
       S_IFLNK    0120000   symbolic link
       S_IFREG    0100000   regular file
       S_IFBLK    0060000   block device
       S_IFDIR    0040000   directory
       S_IFCHR    0020000   character device
       S_IFIFO    0010000   FIFO
       S_ISUID    0004000   set UID bit
       S_ISGID    0002000   set-group-ID bit (see below)
       S_ISVTX    0001000   sticky bit (see below)
       S_IRWXU    00700     mask for file owner permissions
       S_IRUSR    00400     owner has read permission
       S_IWUSR    00200     owner has write permission
       S_IXUSR    00100     owner has execute permission
       S_IRWXG    00070     mask for group permissions
       S_IRGRP    00040     group has read permission
       S_IWGRP    00020     group has write permission
       S_IXGRP    00010     group has execute permission
       S_IRWXO    00007     mask for permissions for others (not in group)
       S_IROTH    00004     others have read permission           
       S_IWOTH    00002     others have write permission
       S_IXOTH    00001     others have execute permission
  • 9
    It might be worth adding to your answer that submodules are listed with a filemode of 160000 and the object type "commit". Aug 2 '10 at 5:15
  • 2
    Why the leading 0 on the top lines (e.g. 0170000 instead of 170000), since it is 0 for all lines, why not just omit it? Aug 22 '14 at 7:47
  • 14
    @CiroSantilli A leading 0 is a classical convention to indicate octal numbers.
    – adl
    Aug 22 '14 at 12:36
  • 8
    This answer is wrong: git does not use all of them, and has a few special ones on its own (submodules have 160000, for example)
    – mirabilos
    Sep 2 '16 at 16:54

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