term% cat index.txt INTRO(2) System Calls Manual 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 ker‐
nel.
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 operations that alter their behavior; see in particular ioctl,
stream, and ttyld(4).
Most system calls have an error return. An error condition is indi‐
cated 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 possible 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 ordinary users to do things al‐
lowed 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
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 ex‐
ist, 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 num‐
ber, 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 temporary condition;
the maximum core size is a system parameter. The error may also
occur if the arrangement of text, data, and stack segments re‐
quires too many segmentation registers.
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 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 at‐
tempt 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 context, 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, men‐
tioning an unknown signal in signal, reading or writing a file
for which seek has generated a negative pointer. Also set by
math functions, see intro(3).
23 ENFILE File table overflow
The system's table of open files is full, and temporarily 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 the
other devices to which these calls apply.
26 ETXTBSY Text file busy
An attempt to execute a pure-procedure program which is cur‐
rently open. Also an attempt to open for writing a pure-proce‐
dure 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 unrepre‐
sentable 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.
INTRO(2)