System call error handling

System calls that fail to complete successfully almost always return a value of -1 to your program. (If you look through the system calls in Section 2, you will see that there are a few calls for which no return value is defined, but they are the exceptions.) In addition to the -1 returned to the program, the unsuccessful system call places an integer in an externally declared variable, errno. In a C program, you can determine the value in errno if your program contains the following statement:

#include <errno.h>

The C language function perror(S) can be used to print an error message (on stderr) based on the value of errno. The value in errno is not cleared on successful calls, so your program should check it only if the system call returned a -1 indicating an error. The following list identifies the error numbers and symbolic names defined in the <errno.h> header file, and described in intro(S).

1 EPERM

Not privileged. Typically this error indicates an attempt to modify a file in some way forbidden except to its owner or a process with the appropriate privilege. It is also returned for attempts by ordinary users to do things allowed only to the super-user.

2 ENOENT

No such file or directory. A file name is specified and the file should exist but fails to, or one of the directories in a path name fails to exist.

3 ESRCH

No such process. No process can be found corresponding to the that specified by PID in thekill orptrace routine.

4 EINTR

Interrupted system call. An asynchronous signal (such as interrupt or quit), which the user has elected to catch, occurred during a system service routine. If execution is resumed after processing the signal, it will appear as if the interrupted routine call returned this error condition.

5 EIO

I/O error. Some physical I/O error has occurred. 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 exists beyond the limit of the device. 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 routines. The argument list limit is 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 appropriate 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 [respectively, write] request is made to a file that is open only for writing (respectively, reading).

10 ECHILD

No child processes. A wait routine was executed by a process that had no existing or unwaited-for child processes.

11 EAGAIN

Resource is temporarily unavailable. For example, the fork routine failed because the system's process table is full or the user is not allowed to create any more processes. Or a system call failed because of insufficient memory or swap space.

12 ENOMEM

Not enough space. During execution of an exec, brk, or sbrk routine, a program asks for more space than the system is able to supply. This is not a temporary condition; the maximum size is a system parameter. 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 thefork routine.

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 use an argument of a routine. For example,errno potentially may be set toEFAULT any time a routine that takes a pointer argument is passed an invalid address, if the system can detect the condition. Because systems 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 file was mentioned where a block device was required (for example, in a call to the mount routine).

16 EBUSY

Device busy. An attempt was made 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). It will also occur if an attempt is made to enable accounting when it is already enabled. The device or resource is currently unavailable.

17 EEXIST

File exists. An existing file was mentioned in an inappropriate context (for example, call to the link routine).

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 operation to a device (for example, 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 prefix or as an argument to the chdir routine).

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 undefined signal in a call to the signal or kill routine. Also set by the functions described in the math package (S).

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).

24 EMFILE

Too many open files. No process may have more than OPEN_MAX file descriptors open at a time.

25 ENOTTY

Not a typewriter. A call was made to theioctl routine specifying a file that is not a special character device.

26 ETXTBSY

Text file busy. 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.

27 EFBIG

File too large. The size of a file exceeded the maximum file size, FCHR_MAX (see getrlimit(S)).

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 thefcntl routine, the setting or removing of record locks on a file cannot be accomplished because there are no more record entries left on the system.

29 ESPIPE

Illegal seek. A call to the lseek routine 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 signal; the error is returned if the signal is ignored.

33 EDOM

Math argument out of domain of func. The argument of a function in the math package is out of the domain of the function.

34 ERANGE

Math result not representable. The value of a function in the math package is not representable within machine precision.

35 ENOMSG

No message of desired type. An attempt was made to receive a message of a type not existing on the specified message queue (see msgop(S)).

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(S), semctl(S), and shmctl(S)).

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. A deadlock situation was detected and avoided. This error pertains to file and record locking.

46 ENOLCK

No record locks available. There are no more locks available. The system lock table is full (see fcntl(S)).

60 ENOSTR

Device not a stream. A putmsg orgetmsg system call was attempted on a file descriptor that is not aSTREAMS device.

61 ENODATA

No data available.

62 ETIME

Timer expired. The timer set for aSTREAMSioctl 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 theioctl operation is indeterminate.

63 ENOSR

Out of stream resources. During a STREAMSopen, either no STREAMS queues or no STREAMS head data structures were available. This is a temporary condition; one may recover from it if other processes release resources.

65 ENOPKG

Package not installed. This error occurs when users attempt to use a system 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.

77 EBADMSG

Not a data message. During aread,getmsg, orioctlI_RECVFD system call to aSTREAMS device, something has come to the head of the queue that cannot be processed. That something depends on the system call: read: control information or a passed file descriptor. getmsg: passed file descriptor. ioctl: control or data information.

78 ENAMETOOLONG

File name too long. The length of the path argument exceedsPATH_MAX, or the length of a path component exceedsNAME_MAX while _POSIX_NO_TRUNC is in effect; (see limits(4)).

79 EOVERFLOW

Value too large to be stored in 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 made to a file that is open only for writing.

82 EREMCHG

Remote address changed.

83 ELIBACC

Cannot access a needed shared library. Trying toexec ana.out that requires a shared library and the shared library doesn't exist or the user doesn't have permission to use it.

84 ELIBBAD

Accessing a corrupted shared library. Trying toexec ana.out that requires a shared library (to be linked in) andexec could not load the shared library. The shared library is probably corrupted.

85 ELIBSCN

.lib section ina.out corrupted Trying toexec ana.out that requires a shared library (to be linked in) and there was erroneous data in the.lib section of thea.out. The.lib section tellsexec what shared libraries are needed. Thea.out is probably corrupted.

86 ELIBMAX

Attempting to link in more shared libraries than system limit. Trying toexec ana.out that requires more static shared libraries than is allowed on the current configuration of the system.

87 ELIBEXEC

Cannotexec a shared library directly. Attempting toexec a shared library directly.

88 EILSEQ

Illegal byte sequence. Handle multiple characters as a single character.

89 ENOSYS

Operation not applicable.

90 ELOOP

Number of symbolic links encountered during path name traversal exceedsMAXSYMLINKS

91 ERESTART

Interrupted system call should be restarted.

92 ESTRPIPE

Streams pipe error (not externally visible).

93 ENOTEMPTY

Directory not empty.

94 EUSERS

Too many users. Too many users.

95 ENOTSOCK

Socket operation on non-socket. Self-explanatory.

96 EDESTADDRREQ

Destination address required. A required address was omitted from an operation on a transport endpoint. Destination address required.

97 EMSGSIZE

Message too long. A message sent on a transport provider 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. For example, trying to accept a connection on a datagram transport endpoint.

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 protocol 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 network.

128 ENETUNREACH

Network is unreachable. Operation was attempted to an unreachable network.

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 internal 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 connected. A connect request was made on an already connected transport endpoint; or, asendto orsendmsg request on a connected transport endpoint specified a destination when already connected.

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 supplied.

143 ESHUTDOWN

Cannot send after transport endpoint shutdown. A request to send data was disallowed because the transport endpoint had already been shut down.

144 ETOOMANYREFS

Too many references: cannot splice.

145 ETIMEDOUT

Connection timed out. A connect or send request failed because the connected party did not properly respond after a period of time. (The timeout period is dependent on the communication protocol.)

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.

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 aconnect) was attempted on a non-blocking object.

151 ESTALE

Stale NFS file handle.

152 ENOLOAD

Cannot load required module. An attempt made to load a module failed.

153 ERELOC

Relocation error in loading module. Symbolic referencing error.

154 ENOMATCH

No symbol is found matching the given spec.

156 EBADVER

Version number mis-matched. The version number associated with a module is not supported by the kernel.

157 ECONFIG

Configured kernel resource exhausted.

158 ECANCELLED

Asynchronous I/O cancelled.