459 lines
16 KiB
Groff
459 lines
16 KiB
Groff
.\" Copyright (c) 1980,1983,1986 Regents of the University of California.
|
|
.\" All rights reserved. The Berkeley software License Agreement
|
|
.\" specifies the terms and conditions for redistribution.
|
|
.\"
|
|
.\" @(#)intro.2 6.7 (Berkeley) 5/23/86
|
|
.\"
|
|
.TH INTRO 2 "June 30, 1986"
|
|
.UC 4
|
|
.de en
|
|
.HP
|
|
\\$1 \\$2 \\$3
|
|
.br
|
|
..
|
|
.SH NAME
|
|
intro, errno \- introduction to system calls and error numbers
|
|
.SH SYNOPSIS
|
|
.B "#include <errno.h>"
|
|
.SH DESCRIPTION
|
|
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 return
|
|
value. This is almost always \-1; the individual descriptions
|
|
specify the details.
|
|
Note that a number of system calls overload the meanings of these
|
|
error numbers, and that the meanings must be interpreted according
|
|
to the type and circumstances of the call.
|
|
.PP
|
|
As with normal arguments, all return codes and values from
|
|
functions are of type integer unless otherwise noted.
|
|
An error number is also made available in the external
|
|
variable \fBerrno\fP, which is not cleared
|
|
on successful calls.
|
|
Thus \fBerrno\fP should be tested only after an error has occurred.
|
|
.PP
|
|
The following is a list of the errors and their
|
|
names as given in
|
|
.RI < sys/errno.h >:
|
|
.en 0 OK "Error 0
|
|
Unused. (The symbol "OK" is only used inside the kernel source.)
|
|
.en 1 EPERM "Not owner
|
|
Typically this error indicates
|
|
an attempt to modify a file in some way forbidden
|
|
except to its owner or super-user.
|
|
It is also returned for attempts
|
|
by ordinary users to do things
|
|
allowed only to the super-user.
|
|
.en 2 ENOENT "No such file or directory
|
|
This error occurs when a file name is specified
|
|
and the file should exist but doesn't, or when one
|
|
of the directories in a path name does not exist.
|
|
.en 3 ESRCH "No such process
|
|
The process or process group whose number was given
|
|
does not exist, or any such process is already dead.
|
|
.en 4 EINTR "Interrupted system call
|
|
An asynchronous signal (such as interrupt or quit)
|
|
that the user has elected to catch
|
|
occurred during a system call.
|
|
If execution is resumed
|
|
after processing the signal
|
|
and the system call is not restarted,
|
|
it will appear as if the interrupted system call
|
|
returned this error condition.
|
|
.en 5 EIO "I/O error
|
|
Some physical I/O error occurred during an I/O operation, usually
|
|
.B read
|
|
or
|
|
.BR write .
|
|
Operations on file descriptors that refer to devices that are forcefully
|
|
taken away or in a bad state will also provoke this error.
|
|
.en 6 ENXIO "No such device or address
|
|
I/O on a special file refers to a subdevice that does not
|
|
exist,
|
|
or beyond the limits of the device.
|
|
It may also occur when, for example, an illegal tape drive
|
|
unit number is selected
|
|
or a disk pack is not loaded on a drive.
|
|
.en 7 E2BIG "Arg list too long
|
|
An argument list longer than ARG_MAX bytes is presented to
|
|
.BR execve .
|
|
ARG_MAX is set to 4096 bytes for 16-bit MINIX 3, 16384 bytes for 32-bit
|
|
MINIX 3, and unlimited for Minix-vmd as these systems are released.
|
|
.en 8 ENOEXEC "Exec format error
|
|
A request is made to execute a file
|
|
that, although it has the appropriate permissions,
|
|
does not start with a valid magic number, (see
|
|
.BR a.out (5)).
|
|
.en 9 EBADF "Bad file number
|
|
Either a file descriptor refers to no
|
|
open file,
|
|
or a read (resp. write) request is made to
|
|
a file that is open only for writing (resp. reading).
|
|
.en 10 ECHILD "No children
|
|
.B Wait
|
|
and the process has no
|
|
living or unwaited-for children.
|
|
.en 11 EAGAIN "Resource temporarily unavailable
|
|
In a
|
|
.B fork,
|
|
the system's process table is full or the user is not allowed to create
|
|
any more processes, otherwise an operation that would cause a process to
|
|
block was attempted on an object in non-blocking mode (see \fBfcntl\fP(2)).
|
|
.en 12 ENOMEM "Not enough core
|
|
During an
|
|
.B execve
|
|
or
|
|
.B brk,
|
|
a program asks for more (virtual) memory than the system is
|
|
able to supply,
|
|
or a process size limit would be exceeded.
|
|
The maximum size
|
|
of the data+stack segment is set by the
|
|
.BR chmem (1)
|
|
program. For Minix-vmd a small data+stack size is increased to 3 megabytes
|
|
when a program is executed.
|
|
.en 13 EACCES "Permission denied
|
|
An attempt was made to access a file in a way forbidden
|
|
by the protection system. Also an attempt to open a device for writing
|
|
that is physically write protected.
|
|
.en 14 EFAULT "Bad address
|
|
An argument of a system call is outside the address space allocated to a
|
|
process.
|
|
.en 15 ENOTBLK "Block device required
|
|
A plain file was mentioned where a block device was required,
|
|
e.g., in
|
|
.BR mount .
|
|
.en 16 EBUSY "Resource busy
|
|
An attempt to mount a device that was already mounted or
|
|
an attempt was made to dismount a device
|
|
on which there is an active file
|
|
(open file, current directory, mounted-on file, or active text segment).
|
|
A request was made to an exclusive access device that was already in use.
|
|
.en 17 EEXIST "File exists
|
|
An existing file was mentioned in an inappropriate context,
|
|
e.g.,
|
|
.BR link .
|
|
.en 18 EXDEV "Cross-device link
|
|
A hard link to a file on another device
|
|
was attempted.
|
|
.en 19 ENODEV "No such device
|
|
An attempt was made to access a device that is not configured by the system,
|
|
i.e., there is no driver for the device.
|
|
.en 20 ENOTDIR "Not a directory
|
|
A non-directory was specified where a directory
|
|
is required,
|
|
for example, in a path name or
|
|
as an argument to
|
|
.BR chdir .
|
|
.en 21 EISDIR "Is a directory
|
|
An attempt to write on a directory.
|
|
.en 22 EINVAL "Invalid argument
|
|
Some invalid argument:
|
|
dismounting a non-mounted
|
|
device,
|
|
mentioning an unknown signal in
|
|
.B signal,
|
|
or some other argument inappropriate for the call.
|
|
Also set by math functions, (see
|
|
.BR math (3)).
|
|
.en 23 ENFILE "File table overflow
|
|
The system's table of open files is full,
|
|
and temporarily no more
|
|
.I opens
|
|
can be accepted.
|
|
.en 24 EMFILE "Too many open files
|
|
The limit on the number of open files per process, OPEN_MAX, is reached.
|
|
As released, this limit is 20 for MINIX 3, and 30 for Minix-vmd.
|
|
.en 25 ENOTTY "Not a typewriter
|
|
The file mentioned in an
|
|
.B ioctl
|
|
is not a terminal or one of the
|
|
devices to which this call applies. (Often seen error from programs with
|
|
bugs in their error reporting code.)
|
|
.en 26 ETXTBSY "Text file busy
|
|
Attempt to execute a program that is open for writing. Obsolete under MINIX 3.
|
|
.en 27 EFBIG "File too large
|
|
The size of a file exceeded the maximum (little over 64 megabytes for
|
|
the V2 file system).
|
|
.en 28 ENOSPC "No space left on device
|
|
A
|
|
.B write
|
|
to an ordinary file, the creation of a
|
|
directory or symbolic link, or the creation of a directory
|
|
entry failed because no more disk blocks are available
|
|
on the file system, or the allocation of an inode for a newly
|
|
created file failed because no more inodes are available
|
|
on the file system.
|
|
.en 29 ESPIPE "Illegal seek
|
|
An
|
|
.B lseek
|
|
was issued to a pipe or TCP/IP channel.
|
|
This error may also be issued for
|
|
other non-seekable devices.
|
|
.en 30 EROFS "Read-only file system
|
|
An attempt to modify a file or directory
|
|
was made
|
|
on a device mounted read-only.
|
|
.en 31 EMLINK "Too many links
|
|
An attempt to make more than a certain number of hard links to a file. The
|
|
advertized maximum, LINK_MAX, is 127, but Minix-vmd uses a much larger
|
|
maximum of 32767 for the V2 file system.
|
|
.en 32 EPIPE "Broken pipe
|
|
A write on a pipe or TCP/IP channel for which there is no process
|
|
to read the data.
|
|
This condition normally generates the signal SIGPIPE;
|
|
the error is returned if the signal is caught or ignored.
|
|
.en 33 EDOM "Math argument
|
|
The argument of a function in the math package
|
|
is out of the domain of the function.
|
|
.en 34 ERANGE "Result too large
|
|
The value of a function in the math package
|
|
is unrepresentable within machine precision.
|
|
.en 35 EDEADLK "Resource deadlock avoided
|
|
A process attempts to place a blocking lock on a file that is already
|
|
locked by another process and that process is waiting for the first
|
|
process to unlock a file that first process already has a lock on.
|
|
(The classic "lock A, lock B" by process 1, and "lock B, lock A" by
|
|
process 2.)
|
|
.en 36 ENAMETOOLONG "File name too long"
|
|
The path name exceeds PATH_MAX characters. PATH_MAX equals 255 as
|
|
distributed.
|
|
.en 37 ENOLCK "No locks available
|
|
The system's table of active locks is full.
|
|
.en 38 ENOSYS "Function not implemented
|
|
The system call is not supported. Either an old program uses an obsolete
|
|
call, or a program for a more capable system is run on a less capable
|
|
system.
|
|
.en 39 ENOTEMPTY "Directory not empty"
|
|
A directory with entries other than \*(lq.\*(rq and \*(lq..\*(rq
|
|
was supplied to a remove directory or rename call.
|
|
.en 40 ELOOP "Too many symbolic links"
|
|
A path name lookup involved too many symbolic links.
|
|
.en 41 ERESTART "Device driver restarted
|
|
.en 43 EIDRM "Identifier removed
|
|
.en 44 EILSEQ "Illegal byte sequence
|
|
.en 50 EPACKSIZE "Invalid packet size
|
|
.en 51 ENOBUFS "Not enough buffers left
|
|
.en 52 EBADIOCTL "Illegal ioctl for device
|
|
.en 53 EBADMODE "Bad mode in ioctl
|
|
.en 54 EWOULDBLOCK "Would block
|
|
.en 55 ENETUNREACH "Network unreachable
|
|
.en 56 EHOSTUNREACH "Host unreachable
|
|
.en 57 EISCONN "Already connected
|
|
.en 58 EADDRINUSE "Address in use
|
|
.en 59 ECONNREFUSED "Connection refused
|
|
.en 60 ECONNRESET "Connection reset
|
|
.en 61 ETIMEDOUT "Connection timed out
|
|
.en 62 EURG "Urgent data present
|
|
.en 63 ENOURG "No urgent data present
|
|
.en 64 ENOTCONN "No connection
|
|
.en 65 ESHUTDOWN "Already shutdown
|
|
.en 66 ENOCONN "No such connection
|
|
.en 67 EAFNOSUPPORT "Address family not supported
|
|
.en 68 EPROTONOSUPPORT "Protocol not supported by AF
|
|
.en 69 EPROTOTYPE "Protocol wrong type for socket
|
|
.en 70 EINPROGRESS "Operation now in progress
|
|
.en 71 EADDRNOTAVAIL "Can't assign requested address
|
|
.en 72 EALREADY "Operation already in progress
|
|
.en 73 EMSGSIZE "Message too long
|
|
.en 74 ENOTSOCK "Socket operation on non-socket
|
|
.en 75 ENOPROTOOPT "Protocol not available
|
|
.en 76 EOPNOTSUPP "Operation not supported
|
|
.en 77 ENETDOWN "Network is down
|
|
.ig
|
|
.en XXX EDQUOT "Disc quota exceeded"
|
|
A
|
|
.B write
|
|
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.
|
|
.en XXX ESTALE "Stale NFS file handle"
|
|
A client referenced a an open file, when the file has been deleted.
|
|
.en XXX EREMOTE "Too many levels of remote in path"
|
|
An attempt was made to remotely mount a file system into a path which
|
|
already has a remotely mounted component.
|
|
..
|
|
.SH DEFINITIONS
|
|
.TP 5
|
|
Process ID
|
|
.br
|
|
Each active process in the system is uniquely identified by a positive
|
|
integer called a process ID. The range of this ID is from 1 to 29999.
|
|
The special process with process ID 1 is
|
|
.BR init ,
|
|
the ancestor of all processes.
|
|
.TP 5
|
|
Parent process ID
|
|
.br
|
|
A new process is created by a currently active process; (see
|
|
.BR fork (2)).
|
|
The parent process ID of a process is the process ID of its creator,
|
|
unless the creator dies, then
|
|
.B init
|
|
becomes the parent of the orphaned process.
|
|
.TP 5
|
|
Process Group ID
|
|
.br
|
|
Each active process is a member of a process group that is identified by
|
|
a positive integer called the process group ID. This is the process
|
|
ID of the group leader. This grouping permits the signaling of related
|
|
processes (see
|
|
.BR kill (2)).
|
|
.TP 5
|
|
Real User ID and Real Group ID
|
|
.br
|
|
Each user on the system is identified by a positive integer
|
|
termed the real user ID.
|
|
.IP
|
|
Each user is also a member of one or more groups.
|
|
One of these groups is distinguished from others and
|
|
used in implementing accounting facilities. The positive
|
|
integer corresponding to this distinguished group is termed
|
|
the real group ID.
|
|
(Under standard MINIX 3 this is the only group a process can be a member of.)
|
|
.IP
|
|
All processes have a real user ID and real group ID.
|
|
These are initialized from the equivalent attributes
|
|
of the process that created it.
|
|
.TP 5
|
|
Effective User Id, Effective Group Id, and Access Groups
|
|
.br
|
|
Access to system resources is governed by three values:
|
|
the effective user ID, the effective group ID, and the
|
|
group access list.
|
|
.IP
|
|
The effective user ID and effective group ID are initially the
|
|
process's real user ID and real group ID respectively. Either
|
|
may be modified through execution of a set-user-ID or set-group-ID
|
|
file (possibly by one its ancestors) (see
|
|
.BR execve (2)).
|
|
.IP
|
|
The group access list is an additional set of group ID's
|
|
used only in determining resource accessibility. Access checks
|
|
are performed as described below in ``File Access Permissions''.
|
|
The maximum number of additional group ID's is NGROUPS_MAX.
|
|
For MINIX 3 this is 0, but Minix-vmd supports a list of up to 16
|
|
additional group ID's. (Also known as ``supplemental'' group ID's.)
|
|
.TP 5
|
|
Super-user
|
|
.br
|
|
A process is recognized as a
|
|
.I super-user
|
|
process and is granted special privileges if its effective user ID is 0.
|
|
.TP 5
|
|
Descriptor
|
|
.br
|
|
An integer assigned by the system when a file or device is referenced
|
|
by
|
|
.BR open (2),
|
|
.BR dup (2)
|
|
or
|
|
.BR fcntl (2)
|
|
which uniquely identifies an access path to that file or device from
|
|
a given process or any of its children.
|
|
.TP 5
|
|
File Descriptor
|
|
Older, and often used name for a descriptor.
|
|
.TP 5
|
|
File Name
|
|
.br
|
|
Names consisting of up to NAME_MAX characters may be used to name
|
|
an ordinary file, special file, or directory. NAME_MAX is the maximum
|
|
of the maximum file name lengths of the supported file systems.
|
|
Excess characters are ignored when too long file names are used for
|
|
files in a given file system.
|
|
The maximum file name length of the V1 and V2 file systems
|
|
is 14 characters. The Minix-vmd "flex" variants of V1 and V2 have a
|
|
60 character maximum.
|
|
.IP
|
|
The characters in a file name may assume any value representable in
|
|
eight bits excluding 0 (null) and the ASCII code for / (slash).
|
|
.IP
|
|
Note that it is generally unwise to use one of \e'"<>();~$^&*|{}[]?
|
|
as part of file names because of the special meaning attached to these
|
|
characters by the shell.
|
|
.TP 5
|
|
Path Name
|
|
.br
|
|
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.
|
|
The total length of a path name must be less than PATH_MAX characters
|
|
(255 as distributed.)
|
|
.IP
|
|
If a path name begins with a slash, the path search begins at the
|
|
.I root
|
|
directory.
|
|
Otherwise, the search begins from the current working directory.
|
|
A slash by itself names the root directory. A null pathname is
|
|
illegal, use "." to refer to the current working directory.
|
|
.TP 5
|
|
Directory
|
|
.br
|
|
A directory is a special type of file that contains entries
|
|
that are references to other files.
|
|
Directory entries are called links. By convention, a directory
|
|
contains at least two links, . and .., referred to as
|
|
.I dot
|
|
and
|
|
.I dot-dot
|
|
respectively. Dot refers to the directory itself and
|
|
dot-dot refers to its parent directory.
|
|
.TP 5
|
|
Root Directory and Current Working Directory
|
|
.br
|
|
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. A process's root directory need not be the root
|
|
directory of the root file system.
|
|
.TP 5
|
|
File Access Permissions
|
|
.br
|
|
Every file in the file system has a set of access permissions.
|
|
These permissions are used in determining whether a process
|
|
may perform a requested operation on the file (such as opening
|
|
a file for writing). Access permissions are established at the
|
|
time a file is created. They may be changed at some later time
|
|
through the
|
|
.BR chmod (2)
|
|
call.
|
|
.IP
|
|
File access is broken down according to whether a file may be: read,
|
|
written, or executed. Directory files use the execute
|
|
permission to control if the directory may be searched.
|
|
.IP
|
|
File access permissions are interpreted by the system as
|
|
they apply to three different classes of users: the owner
|
|
of the file, those users in the file's group, anyone else.
|
|
Every file has an independent set of access permissions for
|
|
each of these classes. When an access check is made, the system
|
|
decides if permission should be granted by checking the access
|
|
information applicable to the caller.
|
|
.IP
|
|
Read, write, and execute/search permissions on
|
|
a file are granted to a process if:
|
|
.IP
|
|
The process's effective user ID is that of the super-user.
|
|
.IP
|
|
The process's effective user ID matches the user ID of the owner
|
|
of the file and the owner permissions allow the access.
|
|
.IP
|
|
The process's effective user ID does not match the user ID of the
|
|
owner of the file, and either the process's effective
|
|
group ID matches the group ID
|
|
of the file, or the group ID of the file is in
|
|
the process's group access list,
|
|
and the group permissions allow the access.
|
|
.IP
|
|
Neither the effective user ID nor effective group ID
|
|
and group access list of the process
|
|
match the corresponding user ID and group ID of the file,
|
|
but the permissions for ``other users'' allow access.
|
|
.IP
|
|
Otherwise, permission is denied.
|
|
.SH SEE ALSO
|
|
.BR intro (3),
|
|
.BR strerror (3).
|