What is the command that will show system boot time messages?

'dmesg' reads and outputs the kernel ring buffer, which captures all messages the kernel generates from boot time onward, including hardware detection, driver initialization, and boot-time errors. It is the standard tool for reviewing what occurred during the system startup sequence.

'echo' simply prints a string to standard output and has no access to kernel or boot messages.

'lspci' lists PCI devices currently detected by the system but does not display boot-time kernel log messages.

'display system boot' is not a valid Linux command.

'messages' is not a standalone executable command; /var/log/messages is a log file that must be read with a command like 'cat' or 'less'.