What does it mean to have a minus sign as the first character of a command in htop output?

Question

In htop, or other commands that show process status, all bash processes have in the command column

/bin/bash

but one process has in the command column

-bash

What does it mean?

Answer 1

A minus sign before the command name is a convention that login programs use to start login shells. A login program is a program where you typically type your password and that starts a session for you, such as login, sudo -i, su -, sshd, etc. A login shell is the initial shell of a text mode session.

Conventionally, when a program invokes another program, it passes the program's name as argument 0; command line arguments are numbered starting from 1. For example, when you run cp foo bar, this executes the executable file located at /bin/cp (on typical systems), and passes cp as argument 0, foo as argument 1 and bar as argument 2. The normal convention is to use the base name of the executable as argument 0. When a login program invokes a shell, it violates this convention and puts an extra hyphen before the program name. Shells understand this alternate convention and set things up appropriately for a login shell, typically reading an initialization file such as ~/.profile, ~/.login, ~/.bash_profile, etc. depending on the shell.

See also Difference between Login Shell and Non-Login Shell?