INTRO(2) INTRO(2)
NAME
intro, errno - introduction to system calls and error
numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
Section 2 of this manual describes all the entries into the
system kernel.
Calls that deal with the file system refer to directory
entries by name. In order to read or write(2) data on a
file, the file must be opened (open, pipe, creat(2)); an
open file is known by a conventional integer value called a
`file descriptor'. Certain open files admit control opera-
tions that alter their behavior; see in particular ioctl,
stream, and ttyld(4).
Most system calls have an error return. An error condition
is indicated by an otherwise impossible returned value.
Almost always this is -1; the individual sections 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
occurred.
There is a table of messages associated with each error, and
a routine for printing the message; see perror(3). The pos-
sible error numbers are not recited with each writeup in
section 2, since many errors are possible for most of the
calls. Here is a list of the error numbers, their names as
defined in <errno.h>, and the messages available using
perror.
0 Error 0
Unused.
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 ordi-
nary users to do things allowed only to the super-user.
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.
3 ESRCH No such process
INTRO(2) INTRO(2)
The process whose number was given to kill does not
exist, or is already dead.
4 EINTR Interrupted system call
An asynchronous signal (such as interrupt or quit),
which the user has elected to catch, occurred during a
system call. If execution is resumed after processing
the signal, it will appear as if the interrupted system
call returned this error condition.
5 EIO I/O error
Some physical I/O error occurred during a read or
write. 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 beyond the limits of the device. It may
also occur when, for example, a tape drive is not
dialed in or no disk pack is loaded on a drive.
7 E2BIG Arg list too long
An argument list longer than 10240 bytes is presented
to exec.
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 magic number, see a.out(5).
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 which is
open only for writing (resp. reading).
10 ECHILD No children
Wait and the process has no living or unwaited-for
children.
11 EAGAIN No more processes
In a fork, the system's process table is full or the
user is not allowed to create any more processes.
12 ENOMEM Not enough core
During an exec or break, a program asks for more core
than the system is able to supply. This is not a tem-
porary condition; the maximum core size is a system
parameter. The error may also occur if the arrangement
of text, data, and stack segments requires too many
segmentation registers.
13 EACCES Permission denied
INTRO(2) INTRO(2)
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 access the arguments of a system call.
15 ENOTBLK Block device required
A plain file was mentioned where a block device was
required, e.g. in mount.
16 EBUSY Mount device 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 directory (open file, current
directory, mounted-on file, active text segment).
17 EEXIST File exists
An existing file was mentioned in an inappropriate con-
text, e.g. link.
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 system
call 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, for example in a path name or as an argument
to chdir.
21 EISDIR Is a directory
An attempt to write on a directory.
22 EINVAL Invalid argument
Some invalid argument: dismounting a non-mounted
device, mentioning an unknown signal in signal, reading
or writing a file for which seek has generated a nega-
tive pointer. Also set by math functions, see
intro(3).
23 ENFILE File table overflow
The system's table of open files is full, and temporar-
ily no more opens can be accepted.
24 EMFILE Too many open files
The limit is 128 per process.
25 ENOTTY Not a typewriter
The file mentioned in ioctl is not a terminal or one of
INTRO(2) INTRO(2)
the other devices to which these calls apply.
26 ETXTBSY Text file busy
An attempt to execute a pure-procedure program which is
currently open. Also an attempt to open for writing a
pure-procedure program that is being executed.
27 EFBIG File too large
The size of a file exceeded the maximum (about 1.0E9
bytes).
28 ENOSPC No space left on device
During a write to an ordinary file, there is no free
space left on the device.
29 ESPIPE Illegal seek
An lseek was issued to a pipe or other non-seekable
device.
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 32767 links 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.
33 EDOM Math argument
The argument of a function in the math package (3M) is
out of the domain of the function.
34 ERANGE Result too large
The value of a function in the math package (3M) is
unrepresentable within machine precision.
35 ELOOP Link loop
An endless cycle of symbolic links was encountered.
SEE ALSO
intro(3)
BUGS
ETXTBSY should happen only when a text file is open for
writing.