Any process group that is not the foreground process group of a session that has established a connection with a controlling terminal.

A session leader that established a connection to a controlling terminal.

A terminal that is associated with a session. Each session may have, at most, one controlling terminal associated with it and a controlling terminal may be associated with only one session. Certain input sequences from the controlling terminal cause signals to be sent to process groups in the session associated with the controlling terminal; see termio(7I).

Directories organize files into a hierarchical system where directories are the nodes in the hierarchy. A directory is a file that catalogs the list of files, including directories (sub-directories), that are directly beneath it in the hierarchy. Entries in a directory file are called links. A link associates a file identifier with a filename. By convention, a directory contains at least two links, . (dot) and .. (dot-dot). The link called dot refers to the directory itself while dot-dot refers to its parent directory. The root directory, which is the top-most node of the hierarchy, has itself as its parent directory. The pathname of the root directory is / and the parent directory of the root directory is /.

In a stream, the direction from stream head to driver.

In a stream, the driver provides the interface between peripheral hardware and the stream. A driver can also be a pseudo-driver, such as a multiplexor or log driver (see log(7D)), which is not associated with a hardware device.

An active process has an effective user ID and an effective group ID that are used to determine file access permissions (see below). The effective user ID and effective group ID are equal to the process's real user ID and real group ID, respectively, unless the process or one of its ancestors evolved from a file that had the set-user-ID bit or set-group-ID bit set (see exec(2)).

Read, write, and execute/search permissions for a file are granted to a process if one or more of the following are true:

• The effective user ID of the process is super-user.
• The effective user ID of the process 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 effective user ID of the process does not match the user ID of the owner of the file, but either the effective group ID or one of the supplementary group IDs of the process match the group ID of the file and the appropriate access bit of the "group" portion (0070) of the file mode is set.
• The effective user ID of the process does not match the user ID of the owner of the file, and neither the effective group ID nor any of the supplementary group IDs of the process match the group ID of the file, but the appropriate access bit of the "other" portion (0007) of the file mode is set.

Otherwise, the corresponding permissions are denied.

A file descriptor is a small integer used to perform I/O on a file. The value of a file descriptor is from 0 to (NOFILES-1). A process may have no more than NOFILES file descriptors open simultaneously. A file descriptor is returned by calls such as open(2) or pipe(2). The file descriptor is used as an argument by calls such as read(2), write(2), ioctl(2), and close(2).

Each file descriptor has a corresponding offset maximum. For regular files that were opened without setting the O_LARGEFILE flag, the offset maximum is 2 Gbyte - 1 byte (2³¹ -1 bytes). For regular files that were opened with the O_LARGEFILE flag set, the offset maximum is 2⁶³ -1 bytes.

Names consisting of 1 to NAME_MAX characters may be used to name an ordinary file, special file or directory.

These characters may be selected from the set of all character values excluding \0 (null) and the ASCII code for / (slash).

Note that it is generally unwise to use *, ?, [, or ] as part of file names because of the special meaning attached to these characters by the shell (see sh(1), csh(1), and ksh(1)). Although permitted, the use of unprintable characters in file names should be avoided.

A file name is sometimes referred to as a pathname component. The interpretation of a pathname component is dependent on the values of NAME_MAX and _POSIX_NO_TRUNC associated with the path prefix of that component. If any pathname component is longer than NAME_MAX and _POSIX_NO_TRUNC is in effect for the path prefix of that component (see fpathconf(2) and limits(4)), it shall be considered an error condition in that implementation. Otherwise, the implementation shall use the first NAME_MAX bytes of the pathname component.

Each session that has established a connection with a controlling terminal will distinguish one process group of the session as the foreground process group of the controlling terminal. This group has certain privileges when accessing its controlling terminal that are denied to background process groups.

Maximum number of entries in a struct iovec array.

The braces notation, {LIMIT}, is used to denote a magnitude limitation imposed by the implementation. This indicates a value which may be defined by a header file (without the braces), or the actual value may be obtained at runtime by a call to the configuration inquiry pathconf(2) with the name argument _PC_LIMIT.

The file mode creation mask of the process used during any create function calls to turn off permission bits in the mode argument supplied. Bit positions that are set in umask(cmask) are cleared in the mode of the created file.

In a stream, one or more blocks of data or information, with associated STREAMS control structures. Messages can be of several defined types, which identify the message contents. Messages are the only means of transferring data and communicating within a stream.

In a stream, a linked list of messages awaiting processing by a module or driver.

A message queue identifier (msqid) is a unique positive integer created by a msgget(2) call. Each msqid has a message queue and a data structure associated with it. The data structure is referred to as msqid_ds and contains the following members:

struct ipc_perm msg_perm; struct msg *msg_first; struct msg *msg_last; ulong_t msg_cbytes; ulong_t msg_qnum; ulong_t msg_qbytes; pid_t msg_lspid; pid_t msg_lrpid; time_t msg_stime; time_t msg_rtime; time_t msg_ctime;

The following are descriptions of the msqid_ds structure members:

The msg_perm member is an ipc_perm structure that specifies the message operation permission (see below). This structure includes the following members:

uid_t cuid; /* creator user id */ gid_t cgid; /* creator group id */ uid_t uid; /* user id */ gid_t gid; /* group id */ mode_t mode; /* r/w permission */ ulong_t seq; /* slot usage sequence # */ key_t key; /* key */

The *msg_first member is a pointer to the first message on the queue.

The *msg_last member is a pointer to the last message on the queue.

The msg_cbytes member is the current number of bytes on the queue.

The msg_qnum member is the number of messages currently on the queue.

The msg_qbytes member is the maximum number of bytes allowed on the queue.

The msg_lspid member is the process ID of the last process that performed a msgsnd() operation.

The msg_lrpid member is the process id of the last process that performed a msgrcv() operation.

The msg_stime member is the time of the last msgsnd() operation.

The msg_rtime member is the time of the last msgrcv() operation.

The msg_ctime member is the time of the last msgctl() operation that changed a member of the above structure.

In the msgctl(2), msgget(2), msgrcv(2), and msgsnd(2) function descriptions, the permission required for an operation is given as {token}, where token is the type of permission needed, interpreted as follows:

00400 READ by user 00200 WRITE by user 00040 READ by group 00020 WRITE by group 00004 READ by others 00002 WRITE by others

Read and write permissions for a msqid are granted to a process if one or more of the following are true:

• The effective user ID of the process is super-user.
• The effective user ID of the process matches msg_perm.cuid or msg_perm.uid in the data structure associated with msqid and the appropriate bit of the "user" portion (0600) of msg_perm.mode is set.
• Any group ID in the process credentials from the set (cr_gid, cr_groups) matches msg_perm.cgid or msg_perm.gid and the appropriate bit of the "group" portion (060) of msg_perm.mode is set.
• The appropriate bit of the "other" portion (006) of msg_perm.mode is set."

Otherwise, the corresponding permissions are denied.

A module is an entity containing processing routines for input and output data. It always exists in the middle of a stream, between the stream's head and a driver. A module is the STREAMS counterpart to the commands in a shell pipeline except that a module contains a pair of functions which allow independent bidirectional (downstream and upstream) data flow and processing.

A multiplexor is a driver that allows streams associated with several user processes to be connected to a single driver, or several drivers to be connected to a single user process. STREAMS does not provide a general multiplexing driver, but does provide the facilities for constructing them and for connecting multiplexed configurations of streams.

An offset maximum is an attribute of an open file description representing the largest value that can be used as a file offset.

A process group in which the parent of every member in the group is either itself a member of the group, or is not a member of the process group's session.

A path name is a null-terminated character string starting with an optional slash (/), followed by zero or more directory names separated by slashes, optionally followed by a file name.

If a path name begins with a slash, the path search begins at the root directory. Otherwise, the search begins from the current working directory.

A slash by itself names the root directory.

Unless specifically stated otherwise, the null path name is treated as if it named a non-existent file.

Each process in the system is uniquely identified during its lifetime by a positive integer called a process ID. A process ID may not be reused by the system until the process lifetime, process group lifetime, and session lifetime ends for any process ID, process group ID, and session ID equal to that process ID. Within a process, there are threads with thread id's, called thread_t and LWPID_t. These threads are not visible to the outside process.

A new process is created by a currently active process (see fork(2)). The parent process ID of a process is the process ID of its creator.

Having appropriate privilege means having the capability to override system restrictions.

Each process in the system is a member of a process group that is identified by a process group ID. Any process that is not a process group leader may create a new process group and become its leader. Any process that is not a process group leader may join an existing process group that shares the same session as the process. A newly created process joins the process group of its parent.

A process group leader is a process whose process ID is the same as its process group ID.

Each active process is a member of a process group and is identified by a positive integer called the process group ID. This ID is the process ID of the group leader. This grouping permits the signaling of related processes (see kill(2)).

A process lifetime begins when the process is forked and ends after it exits, when its termination has been acknowledged by its parent process. See wait(2).

A process group lifetime begins when the process group is created by its process group leader, and ends when the lifetime of the last process in the group ends or when the last process in the group leaves the group.

The processors in a system may be divided into subsets, known as processor sets. A process bound to one of these sets will run only on processors in that set, and the processors in the set will normally run only processes that have been bound to the set. Each active processor set is identified by a positive integer. See pset_create(2).

In a stream, the message queue in a module or driver containing messages moving upstream.

Each user allowed on the system is identified by a positive integer (0 to MAXUID) called a real user ID.

Each user is also a member of a group. The group is identified by a positive integer called the real group ID.

An active process has a real user ID and real group ID that are set to the real user ID and real group ID, respectively, of the user responsible for the creation of the process.

Each process has associated with it a concept of a root directory and a current working directory for the purpose of resolving path name searches. The root directory of a process need not be the root directory of the root file system.

Saved resource limits is an attribute of a process that provides some flexibility in the handling of unrepresentable resource limits, as described in the exec family of functions and setrlimit(2).

The saved user ID and saved group ID are the values of the effective user ID and effective group ID just after an exec of a file whose set user or set group file mode bit has been set (see exec(2)).

A semaphore identifier (semid) is a unique positive integer created by a semget(2) call. Each semid has a set of semaphores and a data structure associated with it. The data structure is referred to as semid_ds and contains the following members:

struct ipc_perm sem_perm; /* operation permission struct */ struct sem *sem_base; /* ptr to first semaphore in set */ ushort_t sem_nsems; /* number of sems in set */ time_t sem_otime; /* last operation time */ time_t sem_ctime; /* last change time */ /* Times measured in secs since */ /* 00:00:00 GMT, Jan. 1, 1970 */

The following are descriptions of the semid_ds structure members:

The sem_perm member is an ipc_perm structure that specifies the semaphore operation permission (see below). This structure includes the following members:

uid_t uid; /* user id */ gid_t gid; /* group id */ uid_t cuid; /* creator user id */ gid_t cgid; /* creator group id */ mode_t mode; /* r/a permission */ ulong_t seq; /* slot usage sequence number */ key_t key; /* key */

The sem_nsems member is equal to the number of semaphores in the set. Each semaphore in the set is referenced by a nonnegative integer referred to as a sem_num. sem_num values run sequentially from 0 to the value of sem_nsems minus 1.

The sem_otime member is the time of the last semop(2) operation.

The sem_ctime member is the time of the last semctl(2) operation that changed a member of the above structure.

A semaphore is a data structure called sem that contains the following members:

ushort_t semval; /* semaphore value */ pid_t sempid; /* pid of last operation */ ushort_t semncnt; /* # awaiting semval > cval */ ushort_t semzcnt; /* # awaiting semval = 0 */

The following are descriptions of the sem structure members:

The semval member is a non-negative integer that is the actual value of the semaphore.

The sempid member is equal to the process ID of the last process that performed a semaphore operation on this semaphore.

The semncnt member is a count of the number of processes that are currently suspended awaiting this semaphore's semval to become greater than its current value.

The semzcnt member is a count of the number of processes that are currently suspended awaiting this semaphore's semval to become 0.

In the semop(2) and semctl(2) function descriptions, the permission required for an operation is given as {token}, where token is the type of permission needed interpreted as follows:

00400	  READ by user
00200   ALTER by user
00040   READ by group
00020   ALTER by group
00004   READ by others
00002   ALTER by others

Read and alter permissions for a semid are granted to a process if one or more of the following are true:

• The effective user ID of the process is super-user.
• The effective user ID of the process matches sem_perm.cuid or sem_perm.uid in the data structure associated with semid and the appropriate bit of the "user" portion (0600) of sem_perm.mode is set.
• The effective group ID of the process matches sem_perm.cgid or sem_perm.gid and the appropriate bit of the "group" portion (060) of sem_perm.mode is set.
• The appropriate bit of the "other" portion (06) of sem_perm.mode is set.

Otherwise, the corresponding permissions are denied.

A session is a group of processes identified by a common ID called a session ID, capable of establishing a connection with a controlling terminal. Any process that is not a process group leader may create a new session and process group, becoming the session leader of the session and process group leader of the process group. A newly created process joins the session of its creator.

Each session in the system is uniquely identified during its lifetime by a positive integer called a session ID, the process ID of its session leader.

A session leader is a process whose session ID is the same as its process and process group ID.

A session lifetime begins when the session is created by its session leader, and ends when the lifetime of the last process that is a member of the session ends, or when the last process that is a member in the session leaves the session.

A shared memory identifier (shmid) is a unique positive integer created by a shmget(2) call. Each shmid has a segment of memory (referred to as a shared memory segment) and a data structure associated with it. (Note that these shared memory segments must be explicitly removed by the user after the last reference to them is removed.) The data structure is referred to as shmid_ds and contains the following members:

struct ipc_perm shm_perm; /* operation permission struct */ size_t shm_segsz; /* size of segment */ struct anon_map *shm_amp; /* ptr to region structure */ char pad[4]; /* for swap compatibility */ pid_t shm_lpid; /* pid of last operation */ pid_t shm_cpid; /* creator pid */ shmatt_t shm_nattch; /* number of current attaches */ ulong_t shm_cnattch; /* used only for shminfo */ time_t shm_atime; /* last attach time */ time_t shm_dtime; /* last detach time */ time_t shm_ctime; /* last change time */ /* Times measured in secs since */ /* 00:00:00 GMT, Jan. 1, 1970 */

The following are descriptions of the shmid_ds structure members:

The shm_perm member is an ipc_perm structure that specifies the shared memory operation permission (see below). This structure includes the following members:

uid_t cuid; /* creator user id */ gid_t cgid; /* creator group id */ uid_t uid; /* user id */ gid_t gid; /* group id */ mode_t mode; /* r/w permission */ ulong_t seq; /* slot usage sequence # */ key_t key; /* key */

The shm_segsz member specifies the size of the shared memory segment in bytes.

The shm_cpid member is the process ID of the process that created the shared memory identifier.

The shm_lpid member is the process ID of the last process that performed a shmat() or shmdt() operation (see shmop(2)).

The shm_nattch member is the number of processes that currently have this segment attached.

The shm_atime member is the time of the last shmat() operation (see shmop(2)).

The shm_dtime member is the time of the last shmdt() operation (see shmop(2)).

The shm_ctime member is the time of the last shmctl(2) operation that changed one of the members of the above structure.

In the shmctl(2), shmat(), and shmdt() (see shmop(2)) function descriptions, the permission required for an operation is given as {token}, where token is the type of permission needed interpreted as follows:

00400 READ by user 00200 WRITE by user 00040 READ by group 00020 WRITE by group 00004 READ by others 00002 WRITE by others

Read and write permissions for a shmid are granted to a process if one or more of the following are true:

• The effective user ID of the process is super-user.
• The effective user ID of the process matches shm_perm.cuid or shm_perm.uid in the data structure associated with shmid and the appropriate bit of the "user" portion (0600) of shm_perm.mode is set.
• The effective group ID of the process matches shm_perm.cgid or shm_perm.gid and the appropriate bit of the "group" portion (060) of shm_perm.mode is set.
• The appropriate bit of the "other" portion (06) of shm_perm.mode is set.

Otherwise, the corresponding permissions are denied.

The process with ID 0 and the process with ID 1 are special processes referred to as proc0 and proc1; see kill(2). proc0 is the process scheduler. proc1 is the initialization process (init); proc1 is the ancestor of every other process in the system and is used to control the process structure.

A set of kernel mechanisms that support the development of network services and data communication drivers. It defines interface standards for character input/output within the kernel and between the kernel and user level processes. The STREAMS mechanism is composed of utility routines, kernel facilities and a set of data structures.

A stream is a full-duplex data path within the kernel between a user process and driver routines. The primary components are a stream head, a driver, and zero or more modules between the stream head and driver. A stream is analogous to a shell pipeline, except that data flow and processing are bidirectional.

In a stream, the stream head is the end of the stream that provides the interface between the stream and a user process. The principal functions of the stream head are processing STREAMS-related system calls and passing data and information between a user process and the stream.

A process is recognized as a super-user process and is granted special privileges, such as immunity from file permissions, if its effective user ID is 0.

In a stream, the direction from driver to stream head.

In a stream, the message queue in a module or driver containing messages moving downstream.