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System Calls Intro(2)
NAME
Intro, intro - introduction to system calls and error
numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
A system call is a C library function that requests a ser-
vice from the system, such as getting the time of day. This
request is performed in the kernel. The library interface
executes a trap into the kernel, which actually executes the
system call code.
Most system calls return one or more error conditions. An
error condition is indicated by an otherwise impossible
return 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, which is not cleared on successful calls, so it
should be tested only after an error has been indicated.
In the case of multithreaded applications, the -mt option
must be specified on the command line at compilation time
(see threads(5)). When the -mt option is specified, errno
becomes a macro that enables each thread to have its own
errno. This errno macro can be used on either side of the
assignment as though it were a variable.
An error value listed as "will fail" describes a condition
whose detection and reporting is mandatory for an implemen-
tation that conforms to the Single UNIX Specification (SUS).
An application can rely on this condition being detected and
reported. An error value listed as "may fail" describes a
condition whose detection and reporting is optional for an
implementation that conforms to the SUS. An application
should not rely this condition being detected and reported.
An application that relies on such behavior cannot be
assured to be portable across conforming implementations.
If more than one error occurs in processing a function call,
any one of the possible errors might may be returned, as the
order of detection is undefined. See standards(5) for addi-
tional information regarding the Single UNIX Specification.
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 Lacking appropriate privileges
Typically this error indicates an
attempt to modify a file in some way
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forbidden except to its owner or an
appropriately privileged process.
It is also returned for attempts by
ordinary users to perform operations
allowed only to processes with cer-
tain privileges.
The manual pages for individual
functions document which privileges
are needed to override the restric-
tion.
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, LWP, or thread
No process can be found in the sys-
tem that corresponds to the speci-
fied PID, LWPID_t, or thread_t.
4 EINTR Interrupted system call
An asynchronous signal (such as
interrupt or quit), which the user
has elected to catch, occurred dur-
ing a system service function. If
execution is resumed after process-
ing the signal, it will appear as if
the interrupted function call
returned this error condition.
In a multithreaded application,
EINTR may be returned whenever
another thread or LWP calls fork(2).
5 EIO I/O error
Some physical I/O error has
occurred. This error may in some
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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 dev-
ice. 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 func-
tions (see exec(2)). 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 appropri-
ate permissions, does not start with
a valid format (see a.out(4)).
9 EBADF Bad file number
Either a file descriptor refers to
no open file, or a read(2) (respec-
tively, write(2)) request is made
to a file that is open only for
writing (respectively, reading).
10 ECHILD No child processes
A wait(3C) function call was
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executed by a process that had no
existing or unwaited-for child
processes.
11 EAGAIN No more processes, or no more LWPs
For example, the fork(2) function
failed because the system's process
table is full or the user is not
allowed to create any more
processes, or a call failed because
of insufficient memory or swap
space.
12 ENOMEM Not enough space
During execution of brk() or sbrk()
(see brk(2)), or one of the exec
family of functions, a program asks
for more space than the system is
able to supply. This is not a tem-
porary condition; the maximum size
is a system parameter. On some
architectures, 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(2) function.
13 EACCES Permission denied
An attempt was made to access a file
in a way forbidden by the protection
system.
The manual pages for individual
functions document which privileges
are needed to override the protec-
tion system.
14 EFAULT Bad address
The system encountered a hardware
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fault in attempting to use an argu-
ment 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 sys-
tems 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 device or file was men-
tioned where a block device was
required (for example, in a call to
the mount(2) function).
16 EBUSY Device busy
An attempt was made to mount a dev-
ice 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 seg-
ment). It will also occur if an
attempt is made to enable accounting
when it is already enabled. The
device or resource is currently una-
vailable. EBUSY is also used by
mutexes, semaphores, condition vari-
ables, and r/w locks, to indicate
that a lock is held, and by the
processor control function
P_ONLINE.
17 EEXIST File exists
An existing file was mentioned in an
inappropriate context (for example,
call to the link(2) function).
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18 EXDEV Cross-device link
A hard 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
(for example, read a write-only dev-
ice).
20 ENOTDIR Not a directory
A non-directory was specified where
a directory is required (for exam-
ple, in a path prefix or as an argu-
ment to the chdir(2) function).
21 EISDIR Is a directory
An attempt was made to write on a
directory.
22 EINVAL Invalid argument
An invalid argument was specified
(for example, unmounting a non-
mounted device), mentioning an unde-
fined signal in a call to the
signal(3C) or kill(2) function, or
an unsupported operation related to
extended attributes was attempted.
23 ENFILE File table overflow
The system file table is full (that
is, SYS_OPEN files are open, and
temporarily no more files can be
opened).
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24 EMFILE Too many open files
No process may have more than
OPEN_MAX file descriptors open at a
time.
25 ENOTTY Inappropriate ioctl for device
A call was made to the ioctl(2)
function specifying a file that is
not a special character device.
26 ETXTBSY Text file busy (obsolete)
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. (This message is
obsolete.)
27 EFBIG File too large
The size of the file exceeded the
limit specified by resource
RLIMIT_FSIZEn; the file size exceeds
the maximum supported by the file
system; or the file size exceeds the
offset maximum of the file descrip-
tor. See the File Descriptor sub-
section of the DEFINITIONS section
below.
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(2) function, the setting
or removing of record locks on a
file cannot be accomplished because
there are no more record entries
left on the system.
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29 ESPIPE Illegal seek
A call to the lseek(2) function 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 sig-
nal; the error is returned if the
signal is ignored.
33 EDOM Math argument out of domain of func-
tion
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
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An attempt was made to receive a
message of a type that does not
exist on the specified message queue
(see msgrcv(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
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A deadlock situation was detected
and avoided. This error pertains to
file and record locking, and also
applies to mutexes, semaphores, con-
dition variables, and r/w locks.
46 ENOLCK No record locks available
There are no more locks available.
The system lock table is full (see
fcntl(2)).
47 ECANCELED Operation canceled
The associated asynchronous opera-
tion was canceled before completion.
48 ENOTSUP Not supported
This version of the system does not
support this feature. Future ver-
sions of the system may provide sup-
port.
49 EDQUOT Disc quota exceeded
A write(2) to an ordinary file, the
creation of a directory or symbolic
link, or the creation of a directory
entry failed because the user's
quota of disk blocks was exhausted,
or the allocation of an inode for a
newly created file failed because
the user's quota of inodes was
exhausted.
58-59 Reserved
60 ENOSTR Device not a stream
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A putmsg(2) or getmsg(2) call was
attempted on a file descriptor that
is not a STREAMS device.
61 ENODATA No data available
62 ETIME Timer expired
The timer set for a STREAMS ioctl(2)
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 indeter-
minate. This is also returned in the
case of _lwp_cond_timedwait(2) or
cond_timedwait(3C).
63 ENOSR Out of stream resources
During a STREAMS open(2) call,
either no STREAMS queues or no
STREAMS head data structures were
available. This is a temporary con-
dition; one may recover from it if
other processes release resources.
65 ENOPKG Package not installed
This error occurs when users attempt
to use a call from a package which
has not been installed.
71 EPROTO Protocol error
Some protocol error occurred. This
error is device-specific, but is
generally not related to a hardware
failure.
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77 EBADMSG Not a data message
During a read(2), getmsg(2), or
ioctl(2) I_RECVFD call to a STREAMS
device, something has come to the
head of the queue that can not be
processed. That something depends
on the call:
read(): control information
or passed file
descriptor.
getmsg(): passed file descrip-
tor.
ioctl(): control or data
information.
78 ENAMETOOLONG File name too long
The length of the path argument
exceeds PATH_MAX, or the length of
a path component exceeds NAME_MAX
while _POSIX_NO_TRUNC is in effect;
see limits.h(3HEAD).
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
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made to a file that is open only for
writing.
82 EREMCHG Remote address changed
83 ELIBACC Cannot access a needed share library
Trying to exec an a.out that
requires a static shared library and
the static shared library does not
exist or the user does not have per-
mission to use it.
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 errone-
ous 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 cor-
rupted.
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 System Administration Guide: IP
Services
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87 ELIBEXEC Cannot exec a shared library
directly
Attempting to exec a shared library
directly.
88 EILSEQ Error 88
Illegal byte sequence. Handle multi-
ple characters as a single charac-
ter.
89 ENOSYS Operation not applicable
90 ELOOP Number of symbolic links encountered
during path name traversal exceeds
MAXSYMLINKS
91 ESTART Restartable system call
Interrupted system call should be
restarted.
92 ESTRPIPE If pipe/FIFO, don't sleep in stream
head
Streams pipe error (not externally
visible).
93 ENOTEMPTY Directory not empty
94 EUSERS Too many users
95 ENOTSOCK Socket operation on non-socket
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96 EDESTADDRREQ Destination address required
A required address was omitted from
an operation on a transport end-
point. Destination address required.
97 EMGSIZE Message too long
A message sent on a transport pro-
vider was larger than the internal
message buffer or some other network
limit.
98 EPROTOTYPE Protocol wrong type for socket
A protocol was specified that does
not support the semantics of the
socket type requested.
99 ENOPROTOOPT Protocol not available
A bad option or level was specified
when getting or setting options for
a protocol.
120 EPROTONOSUPPORT Protocol not supported
The protocol has not been configured
into the system or no implementation
for it exists.
121 ESOCKTNOSUPPORT Socket type not supported
The support for the socket type has
not been configured into the system
or no implementation for it exists.
122 EOPNOTSUPP Operation not supported on transport
endpoint
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For example, trying to accept a con-
nection on a datagram transport end-
point.
123 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.
124 EAFNOSUPPORT Address family not supported by pro-
tocol family
An address incompatible with the
requested protocol was used.
125 EADDRINUSE Address already in use
User attempted to use an address
already in use, and the protocol
does not allow this.
126 EADDRNOTAVAIL Cannot assign requested address
Results from an attempt to create a
transport endpoint with an address
not on the current machine.
127 ENETDOWN Network is down
Operation encountered a dead net-
work.
128 ENETUNREACH Network is unreachable
Operation was attempted to an
unreachable network.
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129 ENETRESET Network dropped connection because
of reset
The host you were connected to
crashed and rebooted.
130 ECONNABORTED Software caused connection abort
A connection abort was caused inter-
nal to your host machine.
131 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.
132 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.
133 EISCONN Transport endpoint is already con-
nected
A connect request was made on an
already connected transport end-
point; or, a sendto(3SOCKET) or
sendmsg(3SOCKET) request on a con-
nected transport endpoint specified
a destination when already con-
nected.
134 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
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supplied.
143 ESHUTDOWN Cannot send after transport endpoint
shutdown
A request to send data was disal-
lowed because the transport endpoint
has already been shut down.
144 ETOOMANYREFS Too many references: cannot splice
145 ETIMEDOUT Connection timed out
A connect(3SOCKET) or
send(3SOCKET) request failed because
the connected party did not properly
respond after a period of time; or a
write(2) or fsync(3C) request
failed because a file is on an NFS
file system mounted with the soft
option.
146 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.
147 EHOSTDOWN Host is down
A transport provider operation
failed because the destination host
was down.
148 EHOSTUNREACH No route to host
A transport provider operation was
attempted to an unreachable host.
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149 EALREADY Operation already in progress
An operation was attempted on a
non-blocking object that already had
an operation in progress.
150 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.
151 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 con-
trolling terminal.
Controlling Process
A session leader that established a connection to a control-
ling 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(7I).
Directory
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 con-
vention, a directory contains at least two links, . (dot)
and .. (dot-dot). The link called dot refers to the direc-
tory 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
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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 peri-
pheral 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.
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 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 for a file are
granted to a process if one or more of the following are
true:
o 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.
o 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.
o 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.
o The read, write, or execute mode bit is not set but the
process has the discretionary file access override
privilege for the corresponding mode bit:
{PRIV_FILE_DAC_READ} for the read bit
{PRIV_FILE_DAC_WRITE} for the write bit,
{PRIV_FILE_DAC_SEARCH} for the execute bit on direc-
tories, and {PRIV_FILE_DAC_EXECUTE} for the executable
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bit on plain files.
Otherwise, the corresponding permissions are denied.
File Descriptor
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 (2
**31 -1 bytes). For regular files that were opened with the
O_LARGEFILE flag set, the offset maximum is 2**63 -1 bytes.
File Name
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 charac-
ter 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 charac-
ters in file names should be avoided.
A file name is sometimes referred to as a pathname com-
ponent. 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.h(3HEAD)), it shall
be considered an error condition in that implementation.
Otherwise, the implementation shall use the first NAME_MAX
bytes of the pathname component.
Foreground Process Group
Each session that has established a connection with a con-
trolling 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
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process groups.
{IOV_MAX}
Maximum number of entries in a struct iovec array.
{LIMIT}
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.
Masks
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.
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 commun-
icating 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(2) call. Each msqid has a mes-
sage queue and a data structure associated with it. The data
structure is referred to as msqid_ds and contains the fol-
lowing 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;
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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() opera-
tion.
The msg_rtime member is the time of the last msgrcv() opera-
tion.
The msg_ctime member is the time of the last msgctl() opera-
tion that changed a member of the above structure.
Message Operation Permissions
In the msgctl(2), msgget(2), msgrcv(2), and msgsnd(2) func-
tion 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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System Calls Intro(2)
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 pro-
cess if one or more of the following are true:
o The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE}
privilege is present in the effective set.
o 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.
o 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.
o The appropriate bit of the "other" portion (006) of
msg_perm.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.
Offset Maximum
An offset maximum is an attribute of an open file descrip-
tion representing the largest value that can be used as a
file offset.
SunOS 5.10 Last change: 4 Oct 2005 24
System Calls Intro(2)
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 direc-
tory 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.
Privileged User
Solaris software implements a set of privileges that provide
fine-grained control over the actions of processes. The pos-
session of of a certain privilege allows a process to per-
form a specific set of restricted operations. Prior to the
Solaris 10 release, a process running with uid 0 was granted
all privileges. See privileges(5) for the semantics and the
degree of backward compatibility awarded to processes with
an effective uid of 0.
Process ID
Each process in the system is uniquely identified during its
lifetime by a positive integer called a process ID. A pro-
cess ID cannot 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. There are threads within a process with
thread IDs thread_t and LWPID_t. These threads are not visi-
ble to the outside process.
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
SunOS 5.10 Last change: 4 Oct 2005 25
System Calls Intro(2)
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 ack-
nowledged by its parent process. See wait(3C).
Process Group Lifetime
A process group lifetime begins when the process group is
created by its process group leader, and ends when the life-
time of the last process in the group ends or when the last
process in the group leaves the group.
Processor Set ID
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 pro-
cessors 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).
Read Queue
In a stream, the message queue in a module or driver con-
taining 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.
Each user is also a member of a group. The group is identi-
fied 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.
SunOS 5.10 Last change: 4 Oct 2005 26
System Calls Intro(2)
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 pro-
cess need not be the root directory of the root file system.
Saved Resource Limits
Saved resource limits is an attribute of a process that pro-
vides some flexibility in the handling of unrepresentable
resource limits, as described in the exec family of func-
tions and setrlimit(2).
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 group ID just after 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(2) call. Each semid has a set of sema-
phores and a data structure associated with it. The data
structure is referred to as semid_ds and contains the fol-
lowing 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 struc-
ture 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
SunOS 5.10 Last change: 4 Oct 2005 27
System Calls Intro(2)
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) opera-
tion.
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.
Semaphore Operation Permissions
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 pro-
cess if one or more of the following are true:
SunOS 5.10 Last change: 4 Oct 2005 28
System Calls Intro(2)
o The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE}
privilege is present in the effective set.
o 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.
o 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.
o The appropriate bit of the "other" portion (06) of
sem_perm.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 pro-
cess 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 pro-
cess 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(2) call. Each shmid has a seg-
ment 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:
SunOS 5.10 Last change: 4 Oct 2005 29
System Calls Intro(2)
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 pro-
cess 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.
Shared Memory Operation Permissions
In the shmctl(2), shmat(), and shmdt() (see shmop(2)) func-
tion descriptions, the permission required for an operation
is given as {token}, where token is the type of permission
SunOS 5.10 Last change: 4 Oct 2005 30
System Calls Intro(2)
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 pro-
cess if one or more of the following are true:
o The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE}
privilege is present in the effective set.
o 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.
o 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.
o The appropriate bit of the "other" portion (06) of
shm_perm.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 pro-
cess (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 com-
ponents 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
SunOS 5.10 Last change: 4 Oct 2005 31
System Calls Intro(2)
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 pro-
cess. The principal functions of the stream head are pro-
cessing STREAMS-related system calls and passing data and
information between a user process and the stream.
Upstream
In a stream, the direction from driver to stream head.
Write Queue
In a stream, the message queue in a module or driver con-
taining messages moving downstream.
SEE ALSO
standards(5), threads(5)
SunOS 5.10 Last change: 4 Oct 2005 32
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