PERMS(3): file permissions and permission checks
__________________________________________________
DESCRIPTION
Files are described by directory entries as described in dir(3).
Read that before reading the description of permission checks
that follows.
Users and groups are defined by the authentication protocol
spoken when dialing file systems. They are a local to each file
tree.
In general, only bits 0777 are honored and their sematics are
those used by UNIX for both files and directories, but for what
follows.
+o Users in the group are granted permission either by the
group bits or by the other bits.
+o The owner is granted permissions by its bits, or the group
bits, or the other bits.
+o When new files or directories are created, their group is
set to that to the containing directory unless a different
one is specified in the system call.
+o The group mode bits for new files and directories are masked
with those of the containing directory, and then any group
bit set in the containing directory is set if it is also set
for the user. (NOTE: not yet for the second edition).
+o Moving a file requires just write permissions in the parent
directories for the old and new locations.
+o Creating a file requires write permission in the file (if it
existed) or in the parent dir (if it did not exist).
+o Only the owner may change the mode of a file.
+o Changing the size using wstat requires write permissions on
the file.
+o Uids (but for wuid) can be changed by the owner but only if
the owner is elf or the owner is also in the target uid.
+o Only the owner or anyone with write permission on a file may
change mtime or other attributes not described before.
When writing new file systems, the convention is to use zxc(1) as
a the reference and [zx/perms(2)] to check for permissions.
SEE ALSO
+o names(3)
+o zx(2)
__________________________________________________
User's manual. Section 3. Copyright © LSUB 2014-2016