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FEXECVE(3)                 Linux Programmer's ManualFEXECVE(3)NAME       fexecve - execute program specified via file descriptorSYNOPSIS       #include <unistd.h>       int fexecve(int fd, char *const argv[], char *const envp[]);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):       fexecve():           Since glibc 2.10:               _POSIX_C_SOURCE >= 200809L           Before glibc 2.10:               _GNU_SOURCEDESCRIPTION       fexecve() performs the same task asexecve(2), with the difference that       the file to be executed is specified via a file descriptor, fd,  rather       than  via  a pathname.  The file descriptor fd must be opened read-only       (O_RDONLY) or with the O_PATH flag and the caller must have  permission       to execute the file that it refers to.RETURN VALUE       A  successful  call to fexecve() never returns.  On error, the function       does return, with a result value of -1, and errno is set appropriately.ERRORS       Errors are as forexecve(2), with the following additions:       EINVAL fd is not a valid file descriptor, or argv is NULL, or  envp  is              NULL.       ENOENT The  close-on-exec flag is set on fd, and fd refers to a script.              See BUGS.       ENOSYS The kernel does not provide theexecveat(2) system call, and the              /proc filesystem could not be accessed.VERSIONS       fexecve() is implemented since glibc 2.3.2.ATTRIBUTES       For  an  explanation  of  the  terms  used  in  this  section,  see at-tributes(7).       +----------+---------------+---------+       |Interface | Attribute     | Value   |       +----------+---------------+---------+       |fexecve() | Thread safety | MT-Safe |       +----------+---------------+---------+CONFORMING TO       POSIX.1-2008.  This function is not specified in POSIX.1-2001,  and  is       not   widely   available   on   other  systems.   It  is  specified  in       POSIX.1-2008.NOTES       On Linux with glibc versions 2.26 and earlier, fexecve() is implemented       using  theproc(5) filesystem, so /proc needs to be mounted and avail-       able at the time of the call.  Since glibc 2.27, if the underlying ker-       nel supports theexecveat(2) system call, then fexecve() is implemented       using that system call, with the benefit that /proc does not need to be       mounted.       The  idea  behind fexecve() is to allow the caller to verify (checksum)       the contents of an executable before executing it.  Simply opening  the       file,  checksumming the contents, and then doing anexecve(2) would not       suffice, since, between the two steps, the  filename,  or  a  directory       prefix  of  the  pathname,  could have been exchanged (by, for example,       modifying the target of a symbolic link).  fexecve() does not  mitigate       the  problem  that  the contents of a file could be changed between the       checksumming and the call to fexecve(); for that, the  solution  is  to       ensure  that the permissions on the file prevent it from being modified       by malicious users.       The natural idiom when using fexecve() is to set the close-on-exec flag       on fd, so that the file descriptor does not leak through to the program       that is executed.  This approach is natural for two reasons.  First, it       prevents  file descriptors being consumed unnecessarily.  (The executed       program normally has no need of a file descriptor that  refers  to  the       program  itself.)   Second, if fexecve() is used recursively, employing       the close-on-exec flag prevents the  file  descriptor  exhaustion  that       would  result from the fact that each step in the recursion would cause       one more file descriptor to be passed to the  new  program.   (But  see       BUGS.)BUGS       If  fd  refers  to  a  script (i.e., it is an executable text file that       names a script interpreter with a first line that begins with the char-       acters  #!)   and the close-on-exec flag has been set for fd, then fex-       ecve() fails with the error ENOENT.  This error occurs because, by  the       time the script interpreter is executed, fd has already been closed be-       cause of the close-on-exec flag.  Thus, the close-on-exec flag can't be       set  on  fd if it refers to a script, leading to the problems described       in NOTES.SEE ALSOexecve(2),execveat(2)COLOPHON       This page is part of release 5.05 of the Linux  man-pages  project.   A       description  of  the project, information about reporting bugs, and the       latest    version    of    this    page,    can     be     found     at       https://www.kernel.org/doc/man-pages/.Linux                             2019-10-10FEXECVE(3)