FMADIO devices run exclusively from pseudo-ROM where any changes on the file system between reboots is lost. This ROM approach provides consistency and system predictability making maintenance simpler.
Shell Environment
One problem with this approach is shell customization becomes quite difficult. To allow small modifications in the shell environment when a user logs into the system it can run the shell script for each SSH session. Configuration file is:
/opt/fmadio/etc/fmadio.rcPlease do not use this excessively, typically its used for setting ENV variables.
Example below
$ cat /opt/fmadio/etc/fmadio.rc
# local shell prompt configuration (ash) ran on at boot time
export TEST="random test variable"Persistent authorized_keys
This file is usually located in ~/.ssh/ directory. As that is part of the volatile file system, the persistent version of this is placed into
/opt/fmadio/etc/authorized_keysThis allows SSH keys to be used in a persistent way across reboots and power cycles. Note the file in /opt/fmadio/etc/authorized_keys is only copied during bootup. Updates made after reboot are not copied to the user .ssh directory.
Custom SSHD config
A customized sshd configuration file can be used by placing the customized configuration into
/opt/fmadio/etc/sshd_config This is helpful for example to force exclusive RSA based login / disable password login. Which is a good practice if the device is on a public network.
Custom SSH RSA ID
In many cases using the default fmadio SSH RSA ID is not a good security practice. As such custom SSH RSA keys both public and private can be copied into
/opt/fmadio/etc/fmadio_id_rsa
/opt/fmadio/etc/fmadio_id_rsa.pubThese will copied into ~/.ssh/idrsa and idrsa_pub on boot
Custom sudoers File
A customized persistant /etc/sudoers file can be created at the following location
/opt/fmadio/etc/sudoersOn boot the system will override the default /etc/sudoers file with the file created per above
/opt/fmadio/etc/sudoers