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_sysctl (2)
  • _sysctl (2) ( Русские man: Системные вызовы )
  • >> _sysctl (2) ( Linux man: Системные вызовы )
  •  

    NAME

    sysctl - read/write system parameters
     
    

    SYNOPSIS

    #include <unistd.h>
    
    #include <linux/sysctl.h> int _sysctl(struct __sysctl_args *args);
     

    DESCRIPTION

    Do not use this system call! See NOTES.

    The _sysctl() call reads and/or writes kernel parameters. For example, the hostname, or the maximum number of open files. The argument has the form

    struct __sysctl_args {
        int    *name;    /* integer vector describing variable */
        int     nlen;    /* length of this vector */
        void   *oldval;  /* 0 or address where to store old value */
        size_t *oldlenp; /* available room for old value,
                            overwritten by actual size of old value */
        void   *newval;  /* 0 or address of new value */
        size_t  newlen;  /* size of new value */
    };
    

    This call does a search in a tree structure, possibly resembling a directory tree under /proc/sys, and if the requested item is found calls some appropriate routine to read or modify the value.  

    RETURN VALUE

    Upon successful completion, _sysctl() returns 0. Otherwise, a value of -1 is returned and errno is set to indicate the error.  

    ERRORS

    EFAULT
    The invocation asked for the previous value by setting oldval non-NULL, but allowed zero room in oldlenp.
    ENOTDIR
    name was not found.
    EPERM
    No search permission for one of the encountered "directories", or no read permission where oldval was non-zero, or no write permission where newval was non-zero.
     

    CONFORMING TO

    This call is Linux-specific, and should not be used in programs intended to be portable. A sysctl() call has been present in Linux since version 1.3.57. It originated in 4.4BSD. Only Linux has the /proc/sys mirror, and the object naming schemes differ between Linux and 4.4BSD, but the declaration of the sysctl() function is the same in both.  

    NOTES

    Glibc does not provide a wrapper for this system call; call it using syscall(2).

    Or rather... don't call it: use of this system call has long been discouraged, and it is so unloved that it is likely to disappear in a future kernel version. Remove it from your programs now; use the /proc/sys interface instead.  

    BUGS

    The object names vary between kernel versions, making this system call worthless for applications.

    Not all available objects are properly documented.

    It is not yet possible to change operating system by writing to /proc/sys/kernel/ostype.  

    EXAMPLE

    #define _GNU_SOURCE
    #include <unistd.h>
    #include <sys/syscall.h>
    #include <string.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <linux/sysctl.h>
    
    int _sysctl(struct __sysctl_args *args );
    
    #define OSNAMESZ 100
    
    int
    main(void)
    {
        struct __sysctl_args args;
        char osname[OSNAMESZ];
        size_t osnamelth;
        int name[] = { CTL_KERN, KERN_OSTYPE };
    
        memset(&args, 0, sizeof(struct __sysctl_args));
        args.name = name;
        args.nlen = sizeof(name)/sizeof(name[0]);
        args.oldval = osname;
        args.oldlenp = &osnamelth;
    
        osnamelth = sizeof(osname);
    
        if (syscall(SYS__sysctl, &args) == -1) {
            perror("_sysctl");
            exit(EXIT_FAILURE);
        }
        printf("This machine is running %*s\n", osnamelth, osname);
        exit(EXIT_SUCCESS);
    }
    
     

    SEE ALSO

    proc(5)  

    COLOPHON

    This page is part of release 3.14 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    RETURN VALUE
    ERRORS
    CONFORMING TO
    NOTES
    BUGS
    EXAMPLE
    SEE ALSO
    COLOPHON


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