Device Nodes

The underlying unix OS that powers the iPhone has a number of device nodes. These nodes can be read from or written to by the OS or applications.

Overview
A iPhone 3G 2.0.2 contains:

crw-rw-rw- 1 root wheel    21,  0 Aug 28 15:35 aes_0 crw--- 1 root wheel    23,  0 Aug 28 18:56 bpf0 crw--- 1 root wheel    23,  1 Aug 28 18:56 bpf1 crw--- 1 root wheel    23,  2 Aug 28 15:35 bpf2 crw--- 1 root wheel    23,  3 Aug 28 15:35 bpf3 c--r-- 1 root wheel    11,  0 Aug 28 15:35 btreset crw--w--w- 1 root wheel     0,  0 Aug 28 15:35 console crw-rw-rw- 1 root wheel     1,  5 Aug 28 18:56 cu.bluetooth crw-rw-rw- 1 root wheel     1,  7 Aug 28 15:35 cu.debug crw-rw-rw- 1 root wheel     1,  1 Aug 28 15:35 cu.iap crw-rw-rw- 1 root wheel     1,  3 Aug 28 15:35 cu.umts brw-r- 1 root operator 14,  0 Aug 28 15:35 disk0 brw-r- 1 root operator 14,  1 Aug 28 15:35 disk0s1 brw-r- 1 root operator 14,  2 Aug 28 15:35 disk0s2 crw--- 1 root wheel     9,  0 Aug 28 15:35 dlci.spi-baseband.0 crw--- 1 root wheel     9,  1 Aug 28 18:56 dlci.spi-baseband.1 crw--- 1 root wheel     9, 10 Aug 28 15:35 dlci.spi-baseband.10 crw--- 1 root wheel     9, 11 Aug 28 15:35 dlci.spi-baseband.11 crw--- 1 root wheel     9, 12 Aug 28 15:35 dlci.spi-baseband.12 crw--- 1 root wheel     9, 13 Aug 28 15:35 dlci.spi-baseband.13 crw--- 1 root wheel     9, 14 Aug 28 15:35 dlci.spi-baseband.14 crw--- 1 root wheel     9, 15 Aug 28 15:35 dlci.spi-baseband.15 crw--- 1 root wheel     9,  2 Aug 28 19:13 dlci.spi-baseband.2 crw--- 1 root wheel     9,  3 Aug 28 18:56 dlci.spi-baseband.3 crw--- 1 root wheel     9,  4 Aug 28 18:56 dlci.spi-baseband.4 crw--- 1 root wheel     9,  5 Aug 28 18:56 dlci.spi-baseband.5 crw--- 1 root wheel     9,  6 Aug 28 18:56 dlci.spi-baseband.6 crw--- 1 root wheel     9,  7 Aug 28 18:56 dlci.spi-baseband.7 crw--- 1 root wheel     9,  8 Aug 28 18:56 dlci.spi-baseband.8 crw--- 1 root wheel     9,  9 Aug 28 18:56 dlci.spi-baseband.9 crw--- 1 root wheel     6,  0 Aug 28 15:35 klog cr--r--r-- 1 root wheel    13,  3 Aug 28 15:35 mrvl868x0 crw--- 1 root wheel     9,  0 Aug 28 15:35 mux.spi-baseband crw-rw-rw- 1 root wheel     3,  2 Aug 28 18:56 null crw-rw-rw- 1 root tty      15,  1 Aug 28 19:13 ptmx crw-rw-rw- 1 root wheel     5,  0 Aug 28 15:35 ptyp0 crw-rw-rw- 1 root wheel     5,  1 Aug 28 15:35 ptyp1 crw-rw-rw- 1 root wheel     5,  2 Aug 28 15:35 ptyp2 crw-rw-rw- 1 root wheel     5,  3 Aug 28 15:35 ptyp3 crw-rw-rw- 1 root wheel     5,  4 Aug 28 15:35 ptyp4 crw-rw-rw- 1 root wheel     5,  5 Aug 28 15:35 ptyp5 crw-rw-rw- 1 root wheel     5,  6 Aug 28 15:35 ptyp6 crw-rw-rw- 1 root wheel     5,  7 Aug 28 15:35 ptyp7 crw-rw-rw- 1 root wheel     8,  0 Aug 28 15:35 random crw-r- 1 root operator 14,  0 Aug 28 15:35 rdisk0 crw-r- 1 root operator 14,  1 Aug 28 15:35 rdisk0s1 crw-r- 1 root operator 14,  2 Aug 28 15:35 rdisk0s2 crw-rw-rw- 1 root wheel    20,  0 Aug 28 15:35 sha1_0 crw-rw-rw- 1 root wheel     2,  0 Aug 28 15:35 tty crw-rw-rw- 1 root wheel     1,  4 Aug 28 15:35 tty.bluetooth crw-rw-rw- 1 root wheel     1,  6 Aug 28 15:35 tty.debug crw-rw-rw- 1 root wheel     1,  0 Aug 28 15:35 tty.iap crw-rw-rw- 1 root wheel     1,  2 Aug 28 15:35 tty.umts crw-rw-rw- 1 root wheel     4,  0 Aug 28 15:35 ttyp0 crw-rw-rw- 1 root wheel     4,  1 Aug 28 15:35 ttyp1 crw-rw-rw- 1 root wheel     4,  2 Aug 28 15:35 ttyp2 crw-rw-rw- 1 root wheel     4,  3 Aug 28 15:35 ttyp3 crw-rw-rw- 1 root wheel     4,  4 Aug 28 15:35 ttyp4 crw-rw-rw- 1 root wheel     4,  5 Aug 28 15:35 ttyp5 crw-rw-rw- 1 root wheel     4,  6 Aug 28 15:35 ttyp6 crw-rw-rw- 1 root wheel     4,  7 Aug 28 15:35 ttyp7 crw--w 1 root tty      16,  0 Aug 28 19:13 ttys000 crw-rw-rw- 1 root wheel    10,  2 Aug 28 15:35 uart.bluetooth crw-rw-rw- 1 root wheel    10,  3 Aug 28 15:35 uart.debug crw-rw-rw- 1 root wheel    10,  0 Aug 28 15:35 uart.iap crw-rw-rw- 1 root wheel    10,  1 Aug 28 15:35 uart.umts crw-rw-rw- 1 root wheel     8,  1 Aug 28 15:35 urandom brw--- 1 root operator  1,  0 Aug 28 15:35 vn0 brw--- 1 root operator  1,  1 Aug 28 15:35 vn1 crw-rw-rw- 1 root wheel     3,  3 Aug 28 15:35 zero

How to access /dev/mem and /dev/kmem
All you need to do is patch the kernel. See here for up to date patches according to the firmware revision that you are on. Basically, the last one patches the setup_kmem flag itself, and the others just patch the checks to it.