ENOSYS(1)			 User Commands			     ENOSYS(1)

NAME
       enosys - utility to make syscalls fail with ENOSYS

SYNOPSIS
       enosys [--syscall|-s syscall] command

DESCRIPTION
       enosys is a simple command to execute a child process for which certain
       syscalls fail with errno ENOSYS.

       It can be used to test the behavior of applications in the face of
       missing syscalls as would happen when running on old kernels.

OPTIONS
       -s, --syscall
	   Syscall to block with ENOSYS. Can be specified multiple times.  An
	   alternative error number or name can be specified with a colon.

       -i, --ioctl
	   Ioctl to block with ENOTTY. Can be specified multiple times.	 An
	   alternative error number or name can be specified with a colon.

       -l, --list
	   List syscalls known to enosys.

       -m, --list-ioctl
	   List ioctls known to enosys.

       -d, --dump[=file]
	   Dump seccomp bytecode filter to standard output.

	   The dump can for example be used by setpriv --seccomp-filter.

       -h, --help
	   Display help text and exit.

       -V, --version
	   Display version and exit.

EXAMPLES
	   # fail syscall "fallocate" with ENOSYS
	   enosys -s fallocate ...

	   # fail syscall "fallocate" with ENOMEM
	   enosys -s fallocate:ENOMEM ...

	   # fail syscall "fallocate" with value 12/ENOMEM
	   enosys -s fallocate:12 ...

	   # fail ioctl FIOCLEX with ENOTTY
	   enosys -i FIOCLEX ...

	   # fail ioctl FIOCLEX with ENOMEM
	   enosys -i FIOCLEX:ENOMEM ...

	   # fail ioctl FIOCLEX with value 12/ENOMEM
	   enosys -i FIOCLEX:12 ...

EXIT STATUS
       enosys exits with the status code of the executed process.  The
       following values have special meanings:

       1
	   internal error

       2
	   system does not provide the necessary functionality

AUTHORS
       Thomas Weißschuh <thomas@t-8ch.de>

SEE ALSO
       syscall(2)

REPORTING BUGS
       For bug reports, use the issue tracker
       <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY
       The enosys command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.41.2		  2025-09-22			     ENOSYS(1)