First steps / Stage 14 of 15

Help and the shell

Not running Starting usually ~20 s

Step 7 of 8 · lab · 15 min

Command not found

User deploy suddenly cannot find even ls. Give the commands back so the fix survives a new login.

Situation

Yesterday a colleague set up the tool utility from /opt/tool/bin for the deploy user. Today almost no command is found in deploy's shell — not even ls and cat, although they work by full path (/usr/bin/ls). tool is not found either.

Enter deploy's shell with sudo -iu deploy, and get back to your own with exit.

Task

Make it so that in a new deploy shell:

the basic commands ls, cat and grep are found by their short names;
tool is found by its short name too.

The check opens a new deploy shell, as on a fresh login: a setting made only in the open terminal is invisible to it.

Lab · on your own

No commands are given in this lab: type them in the terminal yourself. Goals are checked on the machine after every command.

Goals

0 of 2

In a new deploy shell, ls, cat and grep are found by name — not done yet
In a new deploy shell, tool is found by name — not done yet

Ctrl+Enter

Starts the machine node1 · Ubuntu 24.04

The machine is starting

Hints

0 of 3

Report a problem

Lab goals

0 of 2

In a new deploy shell, ls, cat and grep are found by name — not done yet
In a new deploy shell, tool is found by name — not done yet

node1 Ubuntu 24.04

Lab goals

0 of 2

In a new deploy shell, ls, cat and grep are found by name — not done yet
In a new deploy shell, tool is found by name — not done yet

Basic commands · picked for this lab

Environment variables and PATH

Cheat sheet

$_ — insert into the terminal

echo "$PATH" its value
env all environment variables
printenv HOME a single variable
export VAR=value for the current session + children
VAR=value cmd for one command only
source ~/.bashrc reload without a new login
permanent: ~/.bashrc (terminal) · ~/.profile (login/SSH) · /etc/environment (system-wide)
systemd: Environment= / EnvironmentFile= ; cron: inside the script

bash

export VAR=value                  # for the current shell and CHILD processes
VAR=value command                 # for one command only
unset VAR                         # remove it
export PATH="$PATH:/opt/bin"      # append a directory to PATH
export PATH="/opt/bin:$PATH"      # ...prepend it (higher priority)
set                               # ALL shell variables (including non-exported)

The difference: a variable without export is visible only to the current shell; with export, it's inherited by processes started from it.

Where to save it (login vs. non-login)

File	When it's read
`~/.bashrc`	interactive non-login shells (a new terminal/tab)
`~/.profile` / `~/.bash_profile`	login shells (SSH login/console login)
`/etc/profile`, `/etc/profile.d/*.sh`	system-wide for login shells
`/etc/environment`	system-wide for everyone (plain `KEY=value`, no `export`)

A subtlety: an SSH login is a login shell (reads ~/.profile), while a new terminal in an already-open session is non-login (reads ~/.bashrc). That's why Ubuntu's ~/.profile sources ~/.bashrc. source file (or .) reloads it without a new login.

command not found, even though the binary exists

Its directory isn't in $PATH. Check echo $PATH; add the directory or call it by its full path. For something freshly installed, sometimes hash -r (reset the path cache) or a new shell helps.

export worked, but disappeared in a new terminal

export only lives in the current session. To make it permanent, add it to ~/.bashrc (terminals) or ~/.profile (login), then source it or log back in.

The variable is set in the terminal but not over SSH (or vice versa)

Different files for login/non-login (see the table). SSH reads ~/.profile, but you set it in ~/.bashrc — move it, or have one source the other.

A script/cron/systemd doesn't see the variable

cron and systemd units do not read your ~/.bashrc. Set it explicitly: Environment=/EnvironmentFile= in the unit, or inside the script itself for cron.

sudo "loses" variables

sudo resets the environment (env_reset). Pass it through: sudo -E cmd (if allowed) or sudo VAR=val cmd (see sudo).

Help and the shell

Situation

Task

Signing in is needed to start the machine

Where to save it (login vs. non-login)

command not found, even though the binary exists

export worked, but disappeared in a new terminal

The variable is set in the terminal but not over SSH (or vice versa)

A script/cron/systemd doesn't see the variable

sudo "loses" variables