Linux and shell basics | Ground Embedded

To work with an embedded Linux board, the file system, permissions, processes and shell scripts have to be second nature. A summary of the commands used most.

File system

Places you visit often in Linux.

Path	Contents
/bin, /usr/bin	Executables
/etc	Configuration files
/dev	Device files (ttyS0, i2c-1, spidev0.0)
/sys	Kernel objects (GPIO, LEDs, driver attributes)
/proc	Processes, system information
/var/log	Logs

In Linux devices are files too. For a serial port you open /dev/ttyS0 and read and write it.

Commands used most

ls -l, cd, cp, mv, rm, cat, less      # files
grep, find                           # searching
ps, top, kill                        # processes
dmesg                                # kernel messages (driver logs)
chmod, chown                         # permissions
ip addr, ping, ssh, scp              # network

RoadmapSee where this note sits in Embedded Linux→

Permissions

-rwxr-x--- is the read, write and execute permission for owner / group / others. If an ordinary user cannot open /dev/i2c-1, add the user to the group or use a udev rule.

Shell scripts

They automate post-boot set-up, log collection and repeated tests.

#!/bin/sh
for i in $(seq 1 100); do
  cat /sys/class/thermal/thermal_zone0/temp >> temp.log
  sleep 1
done

What is unfamiliar to an MCU developer is that "several programs run at once and the operating system manages the resources". Hardware is touched only through kernel drivers.