Finding out what is going on in your system

Boot

dmesg Log Boot Messages

Processor

cat /proc/version Version of the Linux kernel.
cat /proc/cpuinfo Information about the processor.
cat /proc/ioports Information about the i/o ports.
cat /proc/dma List of the used DMA-channels.
cat /proc/devices List of the importand driver.
cat /proc/interrupts Information about the interrupts.
cat /proc/pci List of the found devices on the PCI bus.
pciprobe PCI check.
cat /proc/stat List of general statistics of the system.

System

ps -auxw Current processes.
cat /proc/meminfo Information about memory.
cat /proc/loadavg Averages load of the system in the last minutes.
cat /proc/uptime Time and idle since the system start in seconds.
cat /proc/scsi/scsi Information about SCSI devices.
fdisk -l Display the detected partitions of hard disks.
lsmod Information about loaded modules. Modules extended the kernel.
cat /dev/sndstat Information about the sound device.
cat /etc/inittab Display the file /etc/inittab. This file contains the start procedures.
ls -R /bin /usr/bin Display the content of the directories /bin and /usr/bin. Here are the general Unix commands. ls -R display the sub directories too.

FileSystem

cat /proc/filesystems List of the supported filesystems.
mount Display the mounted file systems.
df Display the free space of the mounted file systems.

Network

ifconfig Display the network interfaces, for example loopback (lo), network cards (eth).
route -n Display every route
ipfwadm -l -I Display the incoming filter rules
ipfwadm -l -O Display the outgoing filter rules
ipfwadm -l -F Display the forwarding rules
ipfwadm -l -A Display the accounting rules
hostname Display the hostname
cat /etc/hosts Display the file /etc/hosts.
cat /etc/resolv.conf Display the file /etc/resolv.conf (Nameserver)
cat /etc/services Display the file /etc/services (Services).