'\" t
.\"     Title: enosys
.\"    Author: [see the "AUTHOR(S)" section]
.\" Generator: Asciidoctor 2.0.26
.\"      Date: 2026-06-09
.\"    Manual: User Commands
.\"    Source: util-linux 2.41.5
.\"  Language: English
.\"
.TH "ENOSYS" "1" "2026-06-09" "util\-linux 2.41.5" "User Commands"
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.ss \n[.ss] 0
.nh
.ad l
.de URL
\fI\\$2\fP <\\$1>\\$3
..
.als MTO URL
.if \n[.g] \{\
.  mso www.tmac
.  am URL
.    ad l
.  .
.  am MTO
.    ad l
.  .
.  LINKSTYLE blue R < >
.\}
.SH "NAME"
enosys \- utility to make syscalls fail with ENOSYS
.SH "SYNOPSIS"
.sp
\fBenosys\fP [\fB\-\-syscall\fP|\fB\-s\fP \fIsyscall\fP] command
.SH "DESCRIPTION"
.sp
\fBenosys\fP is a simple command to execute a child process for which certain
syscalls fail with errno ENOSYS.
.sp
It can be used to test the behavior of applications in the face of missing
syscalls as would happen when running on old kernels.
.SH "OPTIONS"
.sp
\fB\-s\fP, \fB\-\-syscall\fP
.RS 4
Syscall to block with \fBENOSYS\fP. Can be specified multiple times.
An alternative error number or name can be specified with a colon.
.RE
.sp
\fB\-i\fP, \fB\-\-ioctl\fP
.RS 4
Ioctl to block with \fBENOTTY\fP. Can be specified multiple times.
An alternative error number or name can be specified with a colon.
.RE
.sp
\fB\-l\fP, \fB\-\-list\fP
.RS 4
List syscalls known to \fBenosys\fP.
.RE
.sp
\fB\-m\fP, \fB\-\-list\-ioctl\fP
.RS 4
List ioctls known to \fBenosys\fP.
.RE
.sp
\fB\-d\fP, \fB\-\-dump\fP[\fB=\fP\fIfile\fP]
.RS 4
Dump seccomp bytecode filter to standard output.
.sp
The dump can for example be used by \fBsetpriv \-\-seccomp\-filter\fP.
.RE
.sp
\fB\-h\fP, \fB\-\-help\fP
.RS 4
Display help text and exit.
.RE
.sp
\fB\-V\fP, \fB\-\-version\fP
.RS 4
Display version and exit.
.RE
.SH "EXAMPLES"
.sp
.if n .RS 4
.nf
.fam C
# fail syscall "fallocate" with ENOSYS
enosys \-s fallocate ...
.fam
.fi
.if n .RE
.sp
.if n .RS 4
.nf
.fam C
# fail syscall "fallocate" with ENOMEM
enosys \-s fallocate:ENOMEM ...
.fam
.fi
.if n .RE
.sp
.if n .RS 4
.nf
.fam C
# fail syscall "fallocate" with value 12/ENOMEM
enosys \-s fallocate:12 ...
.fam
.fi
.if n .RE
.sp
.if n .RS 4
.nf
.fam C
# fail ioctl FIOCLEX with ENOTTY
enosys \-i FIOCLEX ...
.fam
.fi
.if n .RE
.sp
.if n .RS 4
.nf
.fam C
# fail ioctl FIOCLEX with ENOMEM
enosys \-i FIOCLEX:ENOMEM ...
.fam
.fi
.if n .RE
.sp
.if n .RS 4
.nf
.fam C
# fail ioctl FIOCLEX with value 12/ENOMEM
enosys \-i FIOCLEX:12 ...
.fam
.fi
.if n .RE
.SH "EXIT STATUS"
.sp
\fBenosys\fP exits with the status code of the executed process.
The following values have special meanings:
.sp
\fB1\fP
.RS 4
internal error
.RE
.sp
\fB2\fP
.RS 4
system does not provide the necessary functionality
.RE
.SH "AUTHORS"
.sp
.MTO "thomas\(att\-8ch.de" "Thomas Weißschuh" ""
.SH "SEE ALSO"
.sp
\fBsyscall\fP(2)
.SH "REPORTING BUGS"
.sp
For bug reports, use the \c
.URL "https://github.com/util\-linux/util\-linux/issues" "issue tracker" "."
.SH "AVAILABILITY"
.sp
The \fBenosys\fP command is part of the util\-linux package which can be downloaded from \c
.URL "https://www.kernel.org/pub/linux/utils/util\-linux/" "Linux Kernel Archive" "."