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.TH BOOTOPTS 5
.SH NAME
bootopts \- ELKS boot time configuration file
.SH SYNOPSIS
.B /bootopts
.SH DESCRIPTION
When ELKS boots, the  partition boot-loader searches for 
.I /linux 
on the root filesystem and loads it. It also searches for the file 
.B /bootopts,
which contains boot options - configuration settings affecting how ELKS starts and runs. 
.PP
A variety of configuration parameters can be set in the /bootopts file
without requiring kernel recompilation.  Very useful for debugging and quick configuration changes.
.PP
.B bootopts
allows e.g. setting the console to be serial (or any other device, such as virtual Alt2 /dev/tty2), 
root mount device (FAT and Minix), read-only/read-write, alternative startup process & args, 
init run level, network start, and set environment variables for the initial startup process, 
such as a shell or shell script. 
Note: if the kernel is compiled with serial console ON, `console=` redirection will have no effect.
.PP
ELKS boot options are specified in a Linux 2.0-style format where newlines are optional
except when it comes to comments: Anything following a hash until the next newline 
is a comment and ignored. Note however that the 
.B bootopts
file may not exceed 511 bytes in length - including comments.
Also note that the file MUST start with 2 hash characters for validation.
.PP
Here's an expanded version of the distribution (default)
.B /bootopts
file, with everything commented out:
.PP
.nf
##      
#console=ttyS0,57600 root=fd0 net=ne0 3 # sercon+multiuser+net
#TZ=MDT7            # timezone
#QEMU=1             # to use ftp/ftpd in qemu
#init=/bin/init 3   # multiuser serial
#init=/bin/sh       # singleuser shell
#LOCALIP=10.0.2.16
#HOSTNAME=elks16
#comirq=,,7,10      # IRQ-settings for COM1-4
#ne0=12,0x300,,0x80
#wd0=10,0x300,0xCC00,0x80
#3c0=11,0x330,,0x80
#buf=8              # L2/EXT buffers (default 64, max 256)
#cache=4            # L1 buffers (default 8, max 20)
#xmsbuf=2975        # number of XMS buffers
#umb=0xC000:0x800,0xD000:0x1000
#sync=30            # seconds per auto-sync
#console=ttyS0,19200 # serial console
#console=tty2       # alt2 console
#root=hda1          # First HD, partition 1
#ro                 # read-only root
#kstack             # kernel stack overflow checking
#strace             # system call tracing
#net=slip
.fi
.PP
Devices can be specified by /dev/ prefix or without, the latter is preferable to save space.
.PP
Of particular importance is the
.I init=
option which tells the kernel which program to start after initialization. The default is
.I /bin/init
which initiates a regular multiuser, multiprocess setting. However, any ELKS program can 
be specified which opens up vast possibilities for both debugging and special purposes (IoT).
In particular, specifying
.B /bin/sash
as the 'init-program' provides a very compact environment to development and debugging, which with a 
compact kernel build may run fine in 256k RAM.
.PP
Non-reserved options without '=' inside them are treated as arguments to 
.I /bin/init or 
the 'init='-program, while options with '=' are passed as environment variables to that process.
.PP
Here are more examples, hopefully self-explanatory:
.PP
.nf
init=/bin/init 3 or just 3
init=/bin/sh HOME=/ TERM=ansi
console=ttyS0, console=/dev/tty2, etc
console=ttyS0,38400
console=tty1
root=fd1, root=/dev/fd1, root=hda[1-4], hdb[1-4], hdc[1-4]
net=eth, net=slip, net=cslip  starts predefined network configurations
ro, rw		The root filesystem may be mounted rw or read only
comirq=,7            sets non-standard IRQ (7) on COM2
.fi
.PP
To edit and adapt
.B bootopts,
either edit the file 
.I elkscmd/rootfs_template/bootopts and run "make" to create another image on the development host, 
or edit 
.B /bootopts
on a  running ELKS system and reboot. Note that 
.B bootopts
is read only once - any change requires a reboot to have effect.
Also not that the device configuration parameters such as 
.I comirq=
and
.I wd0=,
may have empty fields (in which case the defaults form the kernel configuration will be used) but
the commas may not be omitted.
.SH FILES
.nf
/bin/init
/bootopts	System configuration file
.fi
.SH BUGS
Not all man pages referenced in the SEE ALSO section below exist yet.
.PP
.B bootopts
and the boot-loader that uses it have severe space constraints and can never be really user friendly.
.SH "SEE ALSO"
.BR net.cnf (5),
.BR setup (8),
.BR tty (4),
.BR mount.cnf (5),
.BR init (8).
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