CMD(3) (emu) CMD(3)
NAME
cmd - interface to host operating system commands
SYNOPSIS
bind -a '#C' /
/cmd/clone
/cmd/n/ctl
/cmd/n/data
/cmd/n/status
DESCRIPTION
The cmd device provides an interface to commands on the host
operating system, when running emu(1). By convention, this
kernel device (#C) is bound to the root directory (with the
-a option).
Opening the clone file provides a handle for starting a com-
mand, managing the command's I/O, and checking the command's
status. It creates or allocates a currently unused direc-
tory, n under /cmd (where n is a decimal integer). It con-
tains the files ctl, data, and status. The file descriptor
returned from the open of clone provides access to the ctl
file of the directory selected by cmd.
Reading ctl via the file descriptor returned from opening
clone provides the directory number, n, which can then be
used to construct filenames for the related files. Writes
to ctl must have the format:
exec oscmd args ...
File offset is ignored for both reading and writing.
Reading data obtains the data that the command writes to its
standard output and standard error. Writing to data sends
the data into the command's standard input.
The read-only status file provides a status line (to a maxi-
mum of 128 bytes) of the format:
cmd/n refcnt state cmd arg ...
where each field separator is a single blank. The meaning of
each field is:
n The cmd directory number.
refcnt
The number (decimal) of open file descriptors for ctl.
CMD(3) (emu) CMD(3)
state
The status of the interface in directory n:
Open Allocated for use but not yet running a com-
mand.
Execute Running a command
Close Command completed. Available for reallocation
via clone.
cmd arg ...
The active command. Output only for state Execute.
Command execution
On Unix systems, the command is run via /bin/sh as follows:
/bin/sh -c 'cmdargs...'
The command will be run using the Unix user and group ID of
the user that started emu(1), unless it was started by the
super-user, in which case cmd attempts to set the Unix user
ID and group ID to those of a Unix user corresponding to the
current Inferno user's name, and failing that, as user and
group nobody.
On Plan 9, the command is run via /bin/rc as follows:
/bin/rc -c 'cmdargs...'
The command will be run using the Plan 9 identity of the
user that started emu(1).
On Windows systems, the command must be a binary executable
(not built into the command interpreter) in the current
path. It is always run with the same Windows user identity
as started emu(1). Furthermore, the ctl file transforms all
slashes not quoted or escaped by backslashes to backslashes
in the command string before executing it.
SOURCE
/emu/devcmd.c
SEE ALSO
emu(1), os(1)
BUGS
Standard output and standard error ideally should not be
mingled.
Exit status should be available.
The maximum length of a command string is 128 bytes.