ENOSYS(1) User Commands ENOSYS(1)

enosys - utility to make syscalls fail with ENOSYS

enosys [--syscall|-s syscall] command

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.

-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.

# 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 ...

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

Thomas Weißschuh <thomas@t-8ch.de>

syscall(2)

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

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/.

2025-03-29 util-linux 2.41