How do I get a list of installed plugins on my server from the client?
It's minecraft_server.1.8.4.jar running on a Linux server.
When using the Vanilla Minecraft server, you cannot install plugins and therefore there will not be any on your server.
On Bukkit / Spigot servers, you can use the
/plugins command as others said in the comments. It also shows which plugins have been enabled successfully (green) and which failed (red).
Additionally, you can look at the
plugins directory in the server folder. Each
.jar-file should represent one plugin. You need file-access to the server though, and I recommend you to use the command.