A terminal emulator (such as xterm, tmux, or emacs) is responsible for displaying a pseudoterminal in a different context (such as an x server, another terminal, or an emacs buffer respectively). Terminals are divided into three types: virtual terminals (on boot or as presented by [C-]A-F<N>), ‘true’ terminals (exposed on serial ports), and pseudoterminals (controlled by other programs). Essentially, you have a virtual terminal running X running Xterm which controls a pseudoterminal with tmux attached controlling another pseudoterminal.

Login shells are a special flag set when launching shells, sometimes. They typically read different settings (e.g. Bash reads ~/.bash_profile instead of ~/.bashrc). Most shells will launch as a login shell if their command name (argv[0]) begins with a hyphen; Bash also allows explicit bash -l to run a login shell.

Essentially, IPv4 addresses[2] are just numbers from 1 to 2147483647, for example 3405804031. However, since address routing is often based on common binary prefix, more intuitive methods like 203.0.113.255 are used. This notation is just a length-4 list of integers from 0 to 255. To convert from an integer to a common IP address, you divide-with-remainder with a constant divisor of 256. For example, 3405804031 /% 256 = (13303921,256), 13303921 /% 256 = (51968,113), 51968 /% 256 = (203,0), and 203 /% 256 = (0,203).[1] Collecting all the remainders in reverse order, then joining them with periods, produces 203.0.113.255. (This notation is just for people to read; aside from parsing code, none of IPv4 uses this notation.) When you enter an IPv4 address, the opposite happens — an expression like ((203 * 256 + 0) * 256 + 113) * 256 + 255, which evaluates to 3405804031, is performed. These octets are just numbers — using 203.000.113.255 or 203.00.113.255 in place of 203.0.113.255 is merely a choice of how to write the address, as 203 * 256 + 0 = 203 * 256 + 000. mraow

[1]: this operation can be omitted; I include it for symmetry. [2]: though all of this holds true for IPv6, I really didn’t feel like going through 128 bits of address