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    The following form allows you to view linux man pages.

    Command:

    setfsuid

    
    
    

    SYNOPSIS

           #include <sys/fsuid.h>
    
           int setfsuid(uid_t fsuid);
    
    
    

    DESCRIPTION

           The system call setfsuid() changes the value of the caller's filesystem
           user ID--the user ID that  the  Linux  kernel  uses  to  check  for  all
           accesses to the filesystem.  Normally, the value of the filesystem user
           ID will shadow the value of the effective user ID.  In  fact,  whenever
           the  effective  user ID is changed, the filesystem user ID will also be
           changed to the new value of the effective user ID.
    
           Explicit calls to setfsuid() and setfsgid(2) are usually used  only  by
           programs such as the Linux NFS server that need to change what user and
           group ID is used for file access without a corresponding change in  the
           real and effective user and group IDs.  A change in the normal user IDs
           for a program such as the NFS server is a security hole that can expose
           it to unwanted signals.  (But see below.)
    
           setfsuid() will succeed only if the caller is the superuser or if fsuid
           matches either the caller's real user ID, effective user ID, saved set-
           user-ID, or current filesystem user ID.
    
    
    

    RETURN VALUE

           On  both success and failure, this call returns the previous filesystem
           user ID of the caller.
    
    
    

    VERSIONS

           This system call is present in Linux since version 1.2.
    
    
    

    CONFORMING TO

           setfsuid() is  Linux-specific  and  should  not  be  used  in  programs
           intended to be portable.
    
    
    

    NOTES

           When glibc determines that the argument is not a valid user ID, it will
           return -1 and set errno to EINVAL without attempting the system call.
    
           At the time when this system call was  introduced,  one  process  could
           send a signal to another process with the same effective user ID.  This
           meant that if a privileged process changed its effective  user  ID  for
           the  purpose of file permission checking, then it could become vulnera-
           ble to receiving signals sent by another  (unprivileged)  process  with
           the  same  user ID.  The filesystem user ID attribute was thus added to
           allow a process to change its user ID for the purposes of file  permis-
           sion checking without at the same time becoming vulnerable to receiving
           unwanted signals.  Since Linux 2.0, signal permission handling is  dif-
           ferent  (see kill(2)), with the result that a process change can change
           its effective user ID without being  vulnerable  to  receiving  signals
           from  unwanted  processes.   Thus,  setfsuid() is nowadays unneeded and
           should be avoided in new applications (likewise for setfsgid(2)).
           the call fails (because the caller lacks the CAP_SETUID capability).
    
    
    

    SEE ALSO

           kill(2), setfsgid(2), capabilities(7), credentials(7)
    
    
    

    Linux 2013-08-08 SETFSUID(2)

    
    
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