intro(2) intro(2)
NAME
intro - introduction to system calls and error numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
The commands in this section should be used along with those listed
in Section 1 of the User's Reference Manual and Sections 1M, 7 and 8
of the System Administrator Manual. References of the form name(1),
(1M), (7) and (8) refer to entries in the above manuals. References
of the form name(2), name(3), name(4) and name(5) refer to entries in
this manual.
Some of the AT&T 3B2 SVR4 documentation set guides include duplicates
of relevant manpages. In this documentation set, all manpages may be
found in the appropriate Reference Manual and, with the exception of
the Programmer's Guide:XWIN Graphical Windowing System, the
Programmer's Guide: OPEN LOOK Graphical User Interface, and the OPEN
LOOK Graphical User Interface User's Guide, are never duplicated in
the guides.
This section describes all of the system calls. Most of these calls
have one or more error returns. An error condition is indicated by
an otherwise impossible returned value. This is almost always -1 or
the NULL pointer; the individual descriptions specify the details.
An error number is also made available in the external variable
errno. errno is not cleared on successful calls, so it should be
tested only after an error has been indicated.
Each system call description attempts to list all possible error
numbers. The following is a complete list of the error numbers and
their names as defined in <errno.h>.
1 EPERM Not super-user
Typically this error indicates an attempt to modify a file in
some way forbidden except to its owner or the super-user. It
is also returned for attempts by ordinary users to do things
allowed only to the super-user.
2 ENOENT No such file or directory
A file name is specified and the file should exist but doesn't,
or one of the directories in a path name does not exist.
3 ESRCH No such process
No process can be found corresponding to that specified by PID
in the kill or ptrace routine.
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4 EINTR Interrupted system call
An asynchronous signal (such as interrupt or quit), which the
user has elected to catch, occurred during a system service
routine. If execution is resumed after processing the signal,
it will appear as if the interrupted routine call returned this
error condition.
5 EIO I/O error
Some physical I/O error has occurred. This error may in some
cases occur on a call following the one to which it actually
applies.
6 ENXIO No such device or address
I/O on a special file refers to a subdevice which does not
exist, or exists beyond the limit of the device. It may also
occur when, for example, a tape drive is not on-line or no disk
pack is loaded on a drive.
7 E2BIG Arg list too long
An argument list longer than ARG_MAX bytes is presented to a
member of the exec family of routines. The argument list limit
is the sum of the size of the argument list plus the size of
the environment's exported shell variables.
8 ENOEXEC Exec format error
A request is made to execute a file which, although it has the
appropriate permissions, does not start with a valid format.
9 EBADF Bad file number
Either a file descriptor refers to no open file, or a read
[respectively, write] request is made to a file that is open
only for writing (respectively, reading).
10 ECHILD No child processes
A wait routine was executed by a process that had no existing
or unwaited-for child processes.
11 EAGAIN No more processes
For example, the fork routine failed because the system's
process table is full or the user is not allowed to create any
more processes, or a system call failed because of insufficient
memory or swap space.
12 ENOMEM Not enough space
During execution of an exec, brk, or sbrk routine, a program
asks for more space than the system is able to supply. This is
not a temporary condition; the maximum size is a system
parameter. The error may also occur if the arrangement of
text, data, and stack segments requires too many segmentation
registers, or if there is not enough swap space during the fork
routine. If this error occurs on a resource associated with
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Remote File Sharing (RFS), it indicates a memory depletion
which may be temporary, dependent on system activity at the
time the call was invoked.
13 EACCES Permission denied
An attempt was made to access a file in a way forbidden by the
protection system.
14 EFAULT Bad address
The system encountered a hardware fault in attempting to use an
argument of a routine. For example, errno potentially may be
set to EFAULT any time a routine that takes a pointer argument
is passed an invalid address, if the system can detect the
condition. Because systems will differ in their ability to
reliably detect a bad address, on some implementations passing
a bad address to a routine will result in undefined behavior.
15 ENOTBLK Block device required
A non-block file was mentioned where a block device was
required (e.g., in a call to the mount routine).
16 EBUSY Device busy
An attempt was made to mount a device that was already mounted
or an attempt was made to unmount a device on which there is an
active file (open file, current directory, mounted-on file,
active text segment). It will also occur if an attempt is made
to enable accounting when it is already enabled. The device or
resource is currently unavailable.
17 EEXIST File exists
An existing file was mentioned in an inappropriate context
(e.g., call to the link routine).
18 EXDEV Cross-device link
A link to a file on another device was attempted.
19 ENODEV No such device
An attempt was made to apply an inappropriate operation to a
device (e.g., read a write-only device).
20 ENOTDIR Not a directory
A non-directory was specified where a directory is required
(e.g., in a path prefix or as an argument to the chdir
routine).
21 EISDIR Is a directory
An attempt was made to write on a directory.
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22 EINVAL Invalid argument
An invalid argument was specified (e.g., unmounting a non-
mounted device), mentioning an undefined signal in a call to
the signal or kill routine.
23 ENFILE File table overflow
The system file table is full (i.e., SYS_OPEN files are open,
and temporarily no more files can be opened).
24 EMFILE Too many open files
No process may have more than OPEN_MAX file descriptors open at
a time.
25 ENOTTY Not a typewriter
A call was made to the ioctl routine specifying a file that is
not a special character device.
26 ETXTBSY Text file busy
An attempt was made to execute a pure-procedure program that is
currently open for writing. Also an attempt to open for
writing or to remove a pure-procedure program that is being
executed.
27 EFBIG File too large
The size of a file exceeded the maximum file size, FCHR_MAX
[see getrlimit].
28 ENOSPC No space left on device
While writing an ordinary file or creating a directory entry,
there is no free space left on the device. In the fcntl
routine, the setting or removing of record locks on a file
cannot be accomplished because there are no more record entries
left on the system.
29 ESPIPE Illegal seek
A call to the lseek routine was issued to a pipe.
30 EROFS Read-only file system
An attempt to modify a file or directory was made on a device
mounted read-only.
31 EMLINK Too many links
An attempt to make more than the maximum number of links,
LINK_MAX, to a file.
32 EPIPE Broken pipe
A write on a pipe for which there is no process to read the
data. This condition normally generates a signal; the error is
returned if the signal is ignored.
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33 EDOM Math argument out of domain of func
The argument of a function in the math package (3M) is out of
the domain of the function.
34 ERANGE Math result not representable
The value of a function in the math package (3M) is not
representable within machine precision.
35 ENOMSG No message of desired type
An attempt was made to receive a message of a type that does
not exist on the specified message queue [see msgop(2)].
36 EIDRM Identifier removed
This error is returned to processes that resume execution due
to the removal of an identifier from the file system's name
space [see msgctl(2), semctl(2), and shmctl(2)].
37 ECHRNG Channel number out of range
38 EL2NSYNC Level 2 not synchronized
39 EL3HLT Level 3 halted
40 EL3RST Level 3 reset
41 ELNRNG Link number out of range
42 EUNATCH Protocol driver not attached
43 ENOCSI No CSI structure available
44 EL2HLT Level 2 halted
45 EDEADLK Deadlock condition
A deadlock situation was detected and avoided. This error
pertains to file and record locking.
46 ENOLCK No record locks available
There are no more locks available. The system lock table is
full [see fcntl(2)].
47-49 Reserved
58-59 Reserved
60 ENOSTR Device not a stream
A putmsg or getmsg system call was attempted on a file
descriptor that is not a STREAMS device.
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61 ENODATA No data available
62 ETIME Timer expired
The timer set for a STREAMS ioctl call has expired. The cause
of this error is device specific and could indicate either a
hardware or software failure, or perhaps a timeout value that
is too short for the specific operation. The status of the
ioctl operation is indeterminate.
63 ENOSR Out of stream resources
During a STREAMS open, either no STREAMS queues or no STREAMS
head data structures were available. This is a temporary
condition; one may recover from it if other processes release
resources.
64 ENONET Machine is not on the network
This error is Remote File Sharing (RFS) specific. It occurs
when users try to advertise, unadvertise, mount, or unmount
remote resources while the machine has not done the proper
startup to connect to the network.
65 ENOPKG Package not installed
This error occurs when users attempt to use a system call from
a package which has not been installed.
66 EREMOTE Object is remote
This error is RFS specific. It occurs when users try to
advertise a resource which is not on the local machine, or try
to mount/unmount a device (or pathname) that is on a remote
machine.
67 ENOLINK Link has been severed
This error is RFS specific. It occurs when the link (virtual
circuit) connecting to a remote machine is gone.
68 EADV Advertise error
This error is RFS specific. It occurs when users try to
advertise a resource which has been advertised already, or try
to stop RFS while there are resources still advertised, or try
to force unmount a resource when it is still advertised.
69 ESRMNT Srmount error
This error is RFS specific. It occurs when an attempt is made
to stop RFS while resources are still mounted by remote
machines, or when a resource is readvertised with a client list
that does not include a remote machine that currently has the
resource mounted.
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70 ECOMM Communication error on send
This error is RFS specific. It occurs when the current process
is waiting for a message from a remote machine, and the virtual
circuit fails.
71 EPROTO Protocol error
Some protocol error occurred. This error is device specific,
but is generally not related to a hardware failure.
74 EMULTIHOP Multihop attempted
This error is RFS specific. It occurs when users try to access
remote resources which are not directly accessible.
76 EDOTDOT Error 76
This error is RFS specific. A way for the server to tell the
client that a process has transferred back from mount point.
77 EBADMSG Not a data message
During a read, getmsg, or ioctl IRECVFD system call to a
STREAMS device, something has come to the head of the queue
that can't be processed. That something depends on the system
call:
read: control information or a passed file descriptor.
getmsg: passed file descriptor.
ioctl: control or data information.
78 ENAMETOOLONG File name too long
The length of the path argument exceeds PATHMAX, or the length
of a path component exceeds NAMEMAX while POSIXNOTRUNC is
in effect; see limits(4).
79 EOVERFLOW
Value too large for defined data type.
80 ENOTUNIQ Name not unique on network
Given log name not unique.
81 EBADFD File descriptor in bad state
Either a file descriptor refers to no open file or a read
request was made to a file that is open only for writing.
82 EREMCHG Remote address changed
83 ELIBACC Cannot access a needed shared library
Trying to exec an a.out that requires a static shared library
and the static shared library doesn't exist or the user doesn't
have permission to use it.
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84 ELIBBAD Accessing a corrupted shared library
Trying to exec an a.out that requires a static shared library
(to be linked in) and exec could not load the static shared
library. The static shared library is probably corrupted.
85 ELIBSCN .lib section in a.out corrupted
Trying to exec an a.out that requires a static shared library
(to be linked in) and there was erroneous data in the .lib
section of the a.out. The .lib section tells exec what static
shared libraries are needed. The a.out is probably corrupted.
86 ELIBMAX Attempting to link in more shared libraries than system
limit
Trying to exec an a.out that requires more static shared
libraries than is allowed on the current configuration of the
system. See the System Administrator's Guide.
87 ELIBEXEC Cannot exec a shared library directly
Attempting to exec a shared library directly.
88 EILSEQ Error 88
Illegal byte sequence. Handle multiple characters as a single
character.
89 ENOSYS Operation not applicable
90 ELOOP Number of symbolic links encountered during path name
traversal exceeds MAXSYMLINKS
91 ESTART Error 91
Interrupted system call should be restarted.
92 ESTRPIPE Error 92
Streams pipe error (not externally visible).
158 ENOTEMPTY Directory not empty
160 EUSERS Too many users
Too many users.
130 ENOTSOCK Socket operation on non-socket
Self-explanatory.
131 EDESTADDRREQ Destination address required
A required address was omitted from an operation on a transport
endpoint. Destination address required.
132 EMSGSIZE Message too long
A message sent on a transport provider was larger than the
internal message buffer or some other network limit.
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133 EPROTOTYPE Protocol wrong type for socket
A protocol was specified that does not support the semantics of
the socket type requested.
134 ENOPROTOOPT Protocol not available
A bad option or level was specified when getting or setting
options for a protocol.
135 EPROTONOSUPPORT Protocol not supported
The protocol has not been configured into the system or no
implementation for it exists.
136 ESOCKTNOSUPPORT Socket type not supported
The support for the socket type has not been configured into
the system or no implementation for it exists.
137 EOPNOTSUPP Operation not supported on transport endpoint
For example, trying to accept a connection on a datagram
transport endpoint.
138 EPFNOSUPPORT Protocol family not supported
The protocol family has not been configured into the system or
no implementation for it exists. Used for the Internet
protocols.
139 EAFNOSUPPORT Address family not supported by protocol family
An address incompatible with the requested protocol was used.
140 EADDRINUSE Address already in use
User attempted to use an address already in use, and the
protocol does not allow this.
141 EADDRNOTAVAIL Cannot assign requested address
Results from an attempt to create a transport endpoint with an
address not on the current machine.
142 ENETDOWN Network is down
Operation encountered a dead network.
143 ENETUNREACH Network is unreachable
Operation was attempted to an unreachable network.
144 ENETRESET Network dropped connection because of reset
The host you were connected to crashed and rebooted.
145 ECONNABORTED Software caused connection abort
A connection abort was caused internal to your host machine.
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146 ECONNRESET Connection reset by peer
A connection was forcibly closed by a peer. This normally
results from a loss of the connection on the remote host due to
a timeout or a reboot.
147 ENOBUFS No buffer space available
An operation on a transport endpoint or pipe was not performed
because the system lacked sufficient buffer space or because a
queue was full.
148 EISCONN Transport endpoint is already connected
A connect request was made on an already connected transport
endpoint; or, a sendto or sendmsg request on a connected
transport endpoint specified a destination when already
connected.
149 ENOTCONN Transport endpoint is not connected
A request to send or receive data was disallowed because the
transport endpoint is not connected and (when sending a
datagram) no address was supplied.
150 ESHUTDOWN Cannot send after transport endpoint shutdown
A request to send data was disallowed because the transport
endpoint has already been shut down.
151 ETOOMANYREFS Too many references: cannot splice
152 ETIMEDOUT Connection timed out
A connect or send request failed because the connected party
did not properly respond after a period of time. (The timeout
period is dependent on the communication protocol.)
153 ECONNREFUSED Connection refused
No connection could be made because the target machine actively
refused it. This usually results from trying to connect to a
service that is inactive on the remote host.
156 EHOSTDOWN Host is down
A transport provider operation failed because the destination
host was down.
157 EHOSTUNREACH No route to host
A transport provider operation was attempted to an unreachable
host.
129 EALREADY Operation already in progress
An operation was attempted on a non-blocking object that
already had an operation in progress.
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128 EINPROGRESS Operation now in progress
An operation that takes a long time to complete (such as a
connect) was attempted on a non-blocking object.
162 ESTALE Stale NFS file handle
DEFINITIONS
Background Process Group
Any process group that is not the foreground process group of a
session that has established a connection with a controlling
terminal.
Controlling Process
A session leader that established a connection to a controlling
terminal.
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(7).
Directory
Directories organize files into a hierarchical system where
directories are the nodes in the hierarchy. A directory is a file
that catalogues 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
/.
Downstream
In a stream, the direction from stream head to driver.
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(7)], which is not associated
with a hardware device.
Effective User ID and Effective Group ID
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
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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)].
File Access Permissions
Read, write, and execute/search permissions on 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.
File Descriptor
A file descriptor is a small integer used to do 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 system calls such as open, or pipe.
The file descriptor is used as an argument by calls such as read,
write, ioctl, and close.
File Name
Names consisting of 1 to NAMEMAX 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)]. 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
NAMEMAX and POSIXNOTRUNC associated with the path prefix of that
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component. If any pathname component is longer than NAMEMAX and
POSIXNOTRUNC 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 NAMEMAX bytes of the pathname component.
Foreground Process Group
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.
Message
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.
Message Queue
In a stream, a linked list of messages awaiting processing by a
module or driver.
Message Queue Identifier
A message queue identifier (msqid) is a unique positive integer
created by a msgget system call. Each msqid has a message queue and
a data structure associated with it. The data structure is referred
to as msqidds and contains the following members:
struct ipcperm msgperm;
struct msg *msgfirst;
struct msg *msglast;
ulong msgcbytes;
ulong msgqnum;
ulong msgqbytes;
pidt msglspid;
pidt msglrpid;
timet msgstime;
long msgsusec;
timet msgrtime;
long msgrusec;
timet msgctime;
long msgcusec;
Here are descriptions of the fields of the msqidds structure:
msgperm is an ipcperm structure that specifies the message
operation permission (see below). This structure includes the
following members:
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uidt cuid; /* creator user id */
gidt cgid; /* creator group id */
uidt uid; /* user id */
gidt gid; /* group id */
modet mode; /* r/w permission */
ushort seq; /* slot usage sequence # */
keyt key; /* key */
*msgfirst is a pointer to the first message on the queue.
*msglast is a pointer to the last message on the queue.
msgcbytes is the current number of bytes on the queue.
msgqnum is the number of messages currently on the queue.
msgqbytes is the maximum number of bytes allowed on the queue.
msglspid is the process ID of the last process that performed
a msgsnd operation.
msglrpid is the process id of the last process that performed
a msgrcv operation.
msgstime and msgsusec are the seconds and microseconds
respectively, of the time of the last msgsnd operation.
msgrtime and msgrusec are the seconds and microseconds
respectively, of the time of the last msgrcv operation.
msgctime and msgcusec are the seconds and microseconds
respectively, of the time of the last msgctp operation that
changed a member of the above structure.
Message Operation Permissions
In the msgop and msgctl system call 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 on a msqid are granted to a process if one
or more of the following are true:
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The effective user ID of the process is super-user.
The effective user ID of the process matches msgperm.cuid or
msgperm.uid in the data structure associated with msqid and
the appropriate bit of the ``user'' portion (0600) of
msgperm.mode is set.
The effective group ID of the process matches msgperm.cgid or
msgperm.gid and the appropriate bit of the ``group'' portion
(060) of msgperm.mode is set.
The appropriate bit of the ``other'' portion (006) of
msgperm.mode is set.
Otherwise, the corresponding permissions are denied.
Module
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.
Multiplexor
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.
Orphaned Process Group
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.
Path Name
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.
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Process ID
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.
Parent Process ID
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.
Privilege
Having appropriate privilege means having the capability to override
system restrictions.
Process Group
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.
Process Group Leader
A process group leader is a process whose process ID is the same as
its process group ID.
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)].
Process Lifetime
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).
Process Group Lifetime
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.
Read Queue
In a stream, the message queue in a module or driver containing
messages moving upstream.
Real User ID and Real Group ID
Each user allowed on the system is identified by a positive integer
(0 to MAXUID) called a real user ID.
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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.
Root Directory and Current Working Directory
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 User ID and Saved Group ID
The saved user ID and saved group ID are the values of the effective
user ID and effective groupID prior to an exec of a file whose set
user or set group file mode bit has been set [see exec(2)].
Semaphore Identifier
A semaphore identifier (semid) is a unique positive integer created
by a semget system call. Each semid has a set of semaphores and a
data structure associated with it. The data structure is referred to
as semidds and contains the following members:
struct ipcperm semperm; /* operation permission struct */
struct sem *sembase; /* ptr to first semaphore in set */
char sempad[2];
ushort semnsems; /* # of sems in set */
timet semotime; /* last semop time */
long semousec; /* in secs and microsecs. */
timet semctime; /* last change time */
long semcusec /* in secs and microsecs. */
Here are descriptions of the fields of the semidds structure:
semperm is an ipcperm structure that specifies the semaphore
operation permission (see below). This structure includes the
following members:
uidt uid; /* user id */
gidt gid; /* group id */
uidt cuid; /* creator user id */
gidt cgid; /* creator group id */
modet mode; /* r/a permission */
ushort seq; /* slot usage sequence number */
keyt key; /* key */
semnsems 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 semnum. semnum values run
sequentially from 0 to the value of semnsems minus 1.
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semotime and semousec are the seconds and microseconds
respectively, of the time of the last semop operation.
semctime and semcusec are the seconds and microseconds
respectively, of the time of the last semctl operation that
changed a member of the above structure.
A semaphore is a data structure called sem that contains the
following members:
ushort semval; /* semaphore value */
pidt sempid; /* pid of last operation */
ushort semncnt; /* # awaiting semval > cval */
ushort semzcnt; /* # awaiting semval = 0 */
semval is a non-negative integer that is the actual value of
the semaphore.
sempid is equal to the process ID of the last process that
performed a semaphore operation on this semaphore.
semncnt is a count of the number of processes that are
currently suspended awaiting this semaphore's semval to become
greater than its current value.
semzcnt is a count of the number of processes that are
currently suspended awaiting this semaphore's semval to become
0.
Semaphore Operation Permissions
In the semop and semctl system call 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 on 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 semperm.cuid or
semperm.uid in the data structure associated with semid and
the appropriate bit of the ``user'' portion (0600) of
semperm.mode is set.
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The effective group ID of the process matches semperm.cgid or
semperm.gid and the appropriate bit of the ``group'' portion
(060) of semperm.mode is set.
The appropriate bit of the ``other'' portion (06) of
semperm.mode is set.
Otherwise, the corresponding permissions are denied.
Session
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.
Session ID
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.
Session Leader
A session leader is a process whose session ID is the same as its
process and process group ID.
Session Lifetime
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.
Shared Memory Identifier
A shared memory identifier (shmid) is a unique positive integer
created by a shmget system 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 shmidds and contains
the following members:
struct ipcperm shmperm; /* operation permission struct */
int shmsegsz; /* size of segment in bytes */
struct anonmap *shmamp; /* segment anonmap pointer*/
pidt shmlpid; /* pid of last operation */
pidt shmcpid; /* pid of creator */
ulong shmnattch; /* used only for shminfo */
ulong shmcnattch; /* used only for shminfo */
timet shmatime; /* last shmat time */
long shmausec; /* in secs and microsecs.*/
timet shmdtime; /* last shmdt time */
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long shmcusec; /* in secs and microsecs. */
timet shmctime /* last change time */
long shmcusec /* in secs and microsecs. */
Here are descriptions of the fields of the shmidds structure:
shmperm is an ipcperm structure that specifies the shared
memory operation permission (see below). This structure
includes the following members:
uidt cuid; /* creator user id */
gidt cgid; /* creator group id */
uidt uid; /* user id */
gidt gid; /* group id */
modet mode; /* r/w permission */
ushort seq; /* slot usage sequence # */
keyt key; /* key */
shmsegsz specifies the size of the shared memory segment in
bytes.
shmcpid is the process ID of the process that created the
shared memory identifier.
shmlpid is the process ID of the last process that performed a
shmop operation.
shmnattch is the number of processes that currently have this
segment attached.
shmotime and shmausec are the seconds and microseconds
respectively, of the time of the last shmat operation.
shmdtime and shmdusec are the seconds and microseconds
respectively, of the time of the last shmdt operation.
shmctime and shmcusec are the seconds and microseconds
respectively, of the time of the last shmctl operation that
changed members of the above structure.
Shared Memory Operation Permissions
In the shmop and shmctl system call descriptions, the permission
required for an operation is given as {token}, where token is the
type of permission needed interpreted as follows:
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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 on 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 shmperm.cuid or
shmperm.uid in the data structure associated with shmid and
the appropriate bit of the ``user'' portion (0600) of
shmperm.mode is set.
The effective group ID of the process matches shmperm.cgid or
shmperm.gid and the appropriate bit of the ``group'' portion
(060) of shmperm.mode is set.
The appropriate bit of the ``other'' portion (06) of
shmperm.mode is set.
Otherwise, the corresponding permissions are denied.
Special Processes
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.
STREAMS
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.
Stream
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.
Stream Head
In a stream, the stream head is the end of the stream that provides
the interface between the stream and a user process. The principle
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functions of the stream head are processing STREAMS-related system
calls, and passing data and information between a user process and
the stream.
Super-user
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.
Upstream
In a stream, the direction from driver to stream head.
Write Queue
In a stream, the message queue in a module or driver containing
messages moving downstream.
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