HP-UX Reference (11i v2 07/12) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

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Epoch
The time period beginning at 0 hours, 0 minutes, 0 seconds, Coordinated Universal Time (UTC)on
January 1, 1970. Increments quantify the amount of time elapsed from the Epoch to the referenced time.
Leap seconds, which occur at irregular intervals, are not reflected in the count of seconds between the
Epoch and the referenced time. (Fourteen leap seconds occurred in the years 1970 through 1988.)
FIFO special file
A type of file. Data written to a FIFO is read on a first-in-first-out basis. Other characteristics are
described in open(2), read(2), write(2) and lseek(2).
file
A stream of bytes that can be written to and/or read from. A file has certain attributes, including permis-
sions and type. File types include regular file, character special file, block special file, FIFO special
file, network special file, directory, and symbolic link. Every file must have a file name that enables
the user (and many of the HP-UX commands) to refer to the contents of the file. The system imposes no
particular structure on the contents of a file, although some programs do. Files can be accessed serially or
randomly (indexed by byte offset). The interpretation of file contents and structure is up to the programs
that access the file.
file access mode
A characteristic of an open file description that determines whether the described file is open for read-
ing, writing, or both. (See open(2).)
file access permissions
Every file in the file hierarchy has a set of access permissions. These permissions are used in determin-
ing whether a process can perform a requested operation on the file (such as opening a file for writing).
Access permissions are established when a file is created via the open(2) or creat(2) system calls, and can be
changed subsequently through the chmod(2) call. These permissions are read by stat(2) or fstat(2).
File access controls whether a file can be read, written, or executed. Directory files use the execute permis-
sion to control whether or not the directory can be searched.
File access permissions are interpreted by the system as they apply to three different classes of users:
the owner of the file, the users in the file’s group, and anyone else ("other"). Every file has an indepen-
dent set of access permissions for each of these classes. When an access check is made, the system decides
if permission should be granted by checking the access information applicable to the caller.
Read, write, and execute/search permissions on a file are granted to a process if any of the following condi-
tions are met:
• The process’s effective user ID is superuser.
• The process’s effective user ID matches the user ID of the owner of the file and the appropriate
access bit of the owner portion (0700) of the file mode is set.
• The process’s effective user ID does not match the user ID of the owner of the file, and either the
process’s effective group ID matches the group ID of the file, or the group ID of the file is in the
process’s group access list, and the appropriate access bit of the group portion (070) of the file mode is
set.
• The process’s effective user ID does not match the user ID of the owner of the file, and the process’s
effective group ID does not match the group ID of the file, and the group ID of the file is not in the
process’s group access list, and the appropriate access bit of the "other" portion (07) of the file mode is
set.
Otherwise, the corresponding permissions are denied.
file descriptor
A small unique, per-process, nonnegative integer identifier that is used to refer to a file opened for reading
and/or writing. Each file descriptor refers to exactly one open file description.
A file descriptor is obtained through system calls such as creat(2), fcntl(2), open(2), pipe(2), or dup(2).
The file descriptor is used as an argument by calls such as read(2), write(2), ioctl(2), and close(2).
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