Which of the following commands is used on the command line to send messages to the syslog systems.

lastlog displays the last login time of all users.

klog is not a standard command for sending messages to syslog; `dmesg` is often used for kernel messages.

logger is a utility that provides an interface to the syslog system call, allowing users to add entries to the system log from scripts or the command line. This is particularly useful for debugging or recording custom events within the system logs.

slog is not a standard Linux command for interacting with syslog.

syslog refers to the system logging daemon or protocol, not a command for sending messages.