Linux System Call Error Codes
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In C programming language, there is no direct support for error handling. You have to detect the failure and handle the error. In C programming language, return values represents success or failure. linux errno example Inside a C program, when a function fails, you should handle the errors accordingly,
Posix Error Codes
or at least record the errors in a log file. When you are running some program on Linux environment, you might linux errno to string notice that it gives some error number. For example, "Error no is : 17", which doesn't really say much. You really need to know what error number 17 means. This article shows all available error errno.h linux kernel numbers along with it descriptions. This article might be a handy reference for you, when you encounter an error number and you would like to know what it means. In C programming language, there is an external variable called "errno". From this errno variable you can use some error handling functions to find out the error description and handle it appropriately. You have to include errno.h header file to use external
Errno.h Windows
variable errno. perror function prints error description in standard error. The strerror function returns a string describing the error code passed in the argument errnum. The following C code snippet tries to open a file through open system call. There are two flags in the open call. O_CREAT flag is to create a file, if the file does not exist. O_EXCL flag is used with O_CREAT, if the file is already exist open call will fail with the proper error number. $ cat fileopen.c #include
DESCRIPTION top The
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value of the call indicated an error (i.e., -1 from most system calls; -1 or NULL from most library functions); a function that succeeds is allowed to change errno. http://www.thegeekstuff.com/2010/10/linux-error-codes/ Valid error numbers are all nonzero; errno is never set to zero by any system call or library function. For some system calls and library functions (e.g., getpriority(2)), -1 is a valid return on success. In such cases, a successful return can be distinguished from an error return by setting errno to zero before the call, and then, if http://man7.org/linux/man-pages/man3/errno.3.html the call returns a status that indicates that an error may have occurred, checking to see if errno has a nonzero value. errno is defined by the ISO C standard to be a modifiable lvalue of type int, and must not be explicitly declared; errno may be a macro. errno is thread-local; setting it in one thread does not affect its value in any other thread. All the error names specified by POSIX.1 must have distinct values, with the exception of EAGAIN and EWOULDBLOCK, which may be the same. Below is a list of the symbolic error names that are defined on Linux. Some of these are marked POSIX.1, indicating that the name is defined by POSIX.1-2001, or C99, indicating that the name is defined by C99. E2BIG Argument list too long (POSIX.1) EACCES Permission denied (POSIX.1) EADDRINUSE Address already in use (POSIX.1) EADDRNOTAVAIL Address not available (POSIX.1) EAFNOSUPPORT Address family not supported (POSIX.1) EAGAIN Resource temporarily unavailable (may be the same value as EWOULDBLOCK) (POSIX.1) EALREADY Connection already in progress (POSIX.1) EBADE Invalid exch
here for a quick overview of the site Help Center Detailed answers to any questions you might http://unix.stackexchange.com/questions/8355/understand-error-codes-in-linux have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with https://www.win.tue.nl/~aeb/linux/lk/lk-4.html us Unix & Linux Questions Tags Users Badges Unanswered Ask Question _ Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and error codes other Un*x-like operating systems. Join them; it only takes a minute: Sign up Here's how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top Understand error codes in Linux up vote 4 down vote favorite I am working on Linux (Kernel Version 2.6.32.28) laptop. After linux system call I inserted/did file io/removed a SD combo card, I got following errors: mmcblk0: error -123 sending status command mmcblk0: error -123 sending read/write command, response 0x0, card status 0x0 mmcblk0: error -123 sending requesting status Now, I would like to understand what these errors mean. As I saw few standard error codes are located in arch/powerpc/boot/stdio.h and other scattered at various other places.. Is there any systematic way in Linux to track (& understand) the error codes (in the source) ? linux system-calls error-handling share|improve this question edited Feb 11 '12 at 0:00 Gilles 372k696761127 asked Feb 28 '11 at 7:02 TheCottonSilk 13327 migrated from stackoverflow.com Feb 28 '11 at 20:33 This question came from our site for professional and enthusiast programmers. add a comment| 4 Answers 4 active oldest votes up vote 5 down vote accepted There are standard error values, defined in errno.h. You can look at this file on your system to see the numerical values. On most systems, they're in /usr/include/errno.h or a file that it inclu
architectures have different numbers. Often, the kernel routine that handles the call foo is called sys_foo. One finds the association between numbers and names in the sys_call_table, for example in arch/i386/kernel/entry.S. Change The world changes and system calls change. Since one must not break old binaries, the semantics associated to any given system call number must remain fully backwards compatible. What happens in practice is one of two things: either one gets a new and improved system call with a new name and number, and the libc routine that used to invoke the old call is changed to use the new one, or the new call (with new number) gets the old name, and the old call gets "old" prefixed to its name. For example, long ago user IDs had 16 bits, today they have 32. __NR_getuid is 24, and __NR_getuid32 is 199, and the former belongs to the 16-bit version of the call, the latter to the 32-bit version. Looking at the associated kernel routines, we find that these are sys_getuid16 and sys_getuid, respectively. (Thus, sys_getuid does not have number __NR_getuid.) Looking at glibc, we find code somewhat like int getuid32_available = UNKNOWN; uid_t getuid(void) { if (getuid32_available == TRUE) return INLINE_SYSCALL(getuid32, 0); if (getuid32_available == UNKNOWN) { uid_t res = INLINE_SYSCALL(getuid32, 0); if (res == 0 || errno != ENOSYS) { getuid32_available = TRUE; return res; } getuid32_available = FALSE; } return INLINE_SYSCALL(getuid, 0); } For an example where the name was moved and the old call got a name prefixed by "old", see __NR_oldolduname, __NR_olduname, __NR_uname, belonging to sys_olduname, sys_uname, sys_newuname, respectively. One also has __NR_oldstat, __NR_stat, __NR_stat64 belonging to sys_stat, sys_newstat, sys_stat64, respectively. And __NR_umount, __NR_umount2 belonging to sys_oldumount, sys_umount, respectively. And __NR_select, __NR__newselect belonging to old_select, sys_select, respectively. These moving names are confusing - now you have been warned: the system call with number