Unix roots: Bell Labs, 1969

This lab is safe on both VMs: you only read system information and create two small files in a new folder, ~/lab04. Each step shows one Unix idea from the story above, still at work in 2026.

1Ask the system what it is

Run this on rocky01, then on ubu01:

uname -s -r -o

You should see something like this on rocky01:

Linux 6.12.0-211.16.1.el10_2.0.1.x86_64 GNU/Linux

And on ubu01:

Linux 7.0.0-15-generic GNU/Linux

uname (Unix name) has been around since the System V days, and scripts still use it to ask “which system am I on?”. The kernel name is Linux, the second field is the kernel version, and the operating system is reported as GNU/Linux, which is the GNU tools plus the Linux kernel you’ll study in Lessons 5 and 6. On macOS or FreeBSD the same command prints Darwin or FreeBSD.

✅ Checkpoint: You can read the kernel name, kernel version and OS name from uname on both VMs.

2Ask which POSIX rules it follows

Run this on rocky01:

getconf _POSIX_VERSION
getconf POSIX2_VERSION
getconf ARG_MAX
getconf LONG_BIT

You should see something like this:

200809
200809
2097152
64

getconf is itself a POSIX tool. 200809 means the C library follows POSIX.1-2008 (a newer library may report a later date), and POSIX2_VERSION is the version of the shell and utilities part. ARG_MAX is the longest command line, in bytes, a program can be started with, which is why a huge rm * can fail with “Argument list too long”. LONG_BIT 64 tells you it’s a 64-bit system.

✅ Checkpoint: getconf returns a six-digit POSIX date on both VMs.

3See “everything is a file”

Run this on rocky01:

ls -l /dev/null /dev/sda
cat /proc/sys/kernel/hostname
echo "this goes nowhere" > /dev/null; echo "exit=$?"

You should see something like this:

crw-rw-rw-. 1 root root 1, 3 Oct 27 10:01 /dev/null
brw-rw----. 1 root disk 8, 0 Oct 27 10:01 /dev/sda
rocky01
exit=0

The first letter of each ls line is the file type: c is a character device and b is a block device, and the two numbers (1, 3 and 8, 0) tell the kernel which driver and which device. Your whole disk is a file you could read with cat, and the host name is a file the kernel makes up on the spot under /proc. That design started on the PDP-7 in 1969, and you’ll use it constantly in Lessons 10 and 42.

✅ Checkpoint: You can tell a character device from a block device in ls -l, and you read the host name from a file.

4Join small tools with pipes

Question: which login shells do the accounts on ubu01 use, and how many of each? No single command answers that, but four small ones do.

Run this on ubu01:

cut -d: -f7 /etc/passwd | sort | uniq -c | sort -rn

You should see something like this:

     27 /usr/sbin/nologin
      2 /bin/bash
      2 /bin/false
      1 /bin/sync

cut takes the seventh field of every line, sort groups equal lines together, uniq -c counts each group and sort -rn puts the biggest number first. None of these tools knows anything about users or shells, which is the point: each does one small job on plain text. The accounts with nologin or false are service accounts that must never get an interactive shell.

✅ Checkpoint: You know how many accounts on ubu01 use /bin/bash.

5Read the family history in the man pages

Section 2 man pages describe system calls, and their HISTORY part says where each call came from. Rocky has these pages after the standard group from Lesson 2 (or sudo dnf install -y man-pages). On Ubuntu they are in a separate package, sudo apt install -y manpages-dev.

Run this on rocky01:

man 2 fork | grep -A1 '^HISTORY'
man 2 select | grep -A2 '^HISTORY'

You should see something like this:

HISTORY
       POSIX.1-2001, SVr4, 4.3BSD.
HISTORY
       select()
              POSIX.1-2001, 4.4BSD (first appeared in 4.2BSD).

fork, which creates every process on your server, is listed in SVr4 and 4.3BSD, both branches of the family, and in POSIX.1-2001. select, used by network servers to wait on many connections, “first appeared in 4.2BSD”, the Berkeley release that brought TCP/IP. Try man 7 standards for the full list of names (V7, 4.2BSD, SVr4, POSIX.1) with dates.

✅ Checkpoint: You found the BSD and System V names in the HISTORY part of two man pages.

6Edit a file the 1969 way, with ed

ed was the editor Thompson wrote for the first Unix, before screens could show a whole page. It still ships with Linux, and its one-letter commands live on in sed and vim. It isn’t always installed, so add it first.

Run this on rocky01 (on ubu01 use sudo apt install -y ed):

sudo dnf install -y ed
mkdir -p ~/lab04 && cd ~/lab04
printf '%s\n' a 'Unix started on a PDP-7 in 1969.' . 'w unix.txt' q | ed

You should see this:

33

Each line of the printf is one ed command: a (append), the text, a single dot to end the text, w to write the file and q to quit. ed answers only with the number of bytes it wrote. Now open the file and change it interactively:

Run this, then type the four lines after it one by one:

ed unix.txt
,p
s/1969/1969 at Bell Labs/
,p
w
q

You should see this:

33
Unix started on a PDP-7 in 1969.
Unix started on a PDP-7 in 1969 at Bell Labs.
46

,p prints every line, s/old/new/ is the same substitute you’ll use in sed and vim, and w reports 46 bytes. If ed only shows a ?, that’s ed telling you something went wrong. Break It 3 shows how to get the reason.

✅ Checkpoint: cat ~/lab04/unix.txt prints the line that ends “at Bell Labs.”

7Find out which shell /bin/sh is

Run this on both VMs:

ls -l /bin/sh

You should see something like this on rocky01:

lrwxrwxrwx. 1 root root 4 Aug 12 09:14 /bin/sh -> bash

And on ubu01:

lrwxrwxrwx 1 root root 4 Apr  8 14:20 /bin/sh -> dash

/bin/sh is the name every Unix has used for the system shell since the Bourne shell in 1979. On Rocky it points to bash, and on Ubuntu to dash, a small, fast shell that accepts POSIX syntax and little else. Scripts that start with #!/bin/sh should only use POSIX features, and the Break-It lab shows what happens when they don’t.

✅ Checkpoint: You know what /bin/sh points to on each VM.