INTRO(2) INTRO(2)
NAME
intro, errno - introduction to system calls and error
numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
Section 2 of this manual lists all the entries into the sys-
tem. Most of these 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 suc-
cessful 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
The process whose number was given to signal and ptrace
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.
INTRO(2) INTRO(2)
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 that does
not exist, or beyond the limits of the device. It may
also occur when, for example, a tape drive is not
dialled in or no disk pack is loaded on a drive.
7 E2BIG Arg list too long
An argument list longer than 5120 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 that 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
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.
INTRO(2) INTRO(2)
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 (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
Customary configuration limit is 20 per process.
25 ENOTTY Not a typewriter
The file mentioned in stty or gtty 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 that is
currently open for writing (or reading!). 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).
INTRO(2) INTRO(2)
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. This error should also
be issued for other non-seekable devices.
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.
SEE ALSO
intro(3)
ASSEMBLER
as /usr/include/sys.s file ...
The PDP11 assembly language interface is given for each sys-
tem call. The assembler symbols are defined in
`/usr/include/sys.s'.
Return values appear in registers r0 and r1; it is unwise to
count on these registers being preserved when no value is
expected. An erroneous call is always indicated by turning
on the c-bit of the condition codes. The error number is
returned in r0. The presence of an error is most easily
tested by the instructions bes and bec (`branch on error set
(or clear)'). These are synonyms for the bcs and bcc
instructions.
On the Interdata 8/32, the system call arguments correspond
well to the arguments of the C routines. The sequence is:
la %2,errno
l %0,&callno
INTRO(2) INTRO(2)
svc 0,args
Thus register 2 points to a word into which the error number
will be stored as needed; it is cleared if no error occurs.
Register 0 contains the system call number; the nomenclature
is identical to that on the PDP11. The argument of the svc
is the address of the arguments, laid out in storage as in
the C calling sequence. The return value is in register 2
(possibly 3 also, as in pipe) and is -1 in case of error.
The overflow bit in the program status word is also set when
errors occur.