waybar does not launch every time with exec-once

[UtkarshVerma]

I am facing a problem where waybar does not lauch reliably for me. I am pretty sure this is a race condition and I am trying to figure out what it could be. I have noticed that even with the default Hyprland config, just adding exec-once = waybar does not launch it.

I wrote a wrapper script for waybar as follows:

#!/bin/sh

exec /usr/sbin/waybar -l info "$@" >"$HOME"/waybar.log 2>&1

What I can see is Hyprland does try to launch it (it also shows up in the Hyprland logs) but the ~/waybar.log file just turns out empty. Moreover, if I start it manually a bit later, then waybar launches instantly and ~/waybar.log is populated with the logs.

It also seems to work by adding a sleep 1 statement so definitely a race condition.

System details

I am using the following build of Hyprland:

Hyprland 0.51.1 built from branch  at commit 71a1216abcc7031776630a6d88f105605c4dc1c9  ([gha] Nix: update inputs).
Date: Mon Sep 22 20:54:03 2025
Tag: v0.51.1, commits: 6436
built against:
 aquamarine 0.9.5
 hyprlang 0.6.3
 hyprutils 0.10.0
 hyprcursor 0.1.13
 hyprgraphics 0.2.0


no flags were set

I launch it using greetd and tuigreet with the following command.

#!/bin/sh

export XDG_SESSION_TYPE=wayland
# Hyprland sets XDG_CURRENT_DESKTOP itself.

exec zsh --login -c Hyprland

My waybar config is nothing special

{
	"reload_style_on_change": true,
	"layer": "bottom", // dmenu must be able to appear over it.
	"position": "top",
	"spacing": 0, // Let CSS specify this.
	"height": 37, // Fix the height so there is not layout shift.
	"margin": "20px 20px 0 20px", // Let Hyprland manage the bottom margin.
	"fixed-center": false, // This is needed for modules-right to grow as required.
	"modules-left": [
		"hyprland/workspaces",
		"hyprland/window"
	],
	"modules-right": [
		// "custom/email",
		"custom/music",
		"custom/disk",
		"custom/memory",
		"custom/swap",
		"custom/cpu",
		"custom/microphone",
		"custom/screen-recording",
		"custom/audio",
		"custom/battery",
		"custom/date",
		"tray"
	],
	// https://github.com/Alexays/Waybar/wiki/Module:-Hyprland#workspaces
	"hyprland/workspaces": {
		"on-click": "activate",
		"format": "{icon}",
		// This is needed for the split-workspace plugin so that workspace
		// names are consistent with what is shown in the bar.
		"format-icons": {
			"1": "1",
			"2": "2",
			"3": "3",
			"4": "4",
			"5": "5",
			"6": "1",
			"7": "2",
			"8": "3",
			"9": "4",
			"10": "5"
		},
		"all-outputs": false
	},
	"hyprland/window": {
		"format": "{title}",
		"icon": true,
		"icon-size": 16,
		"tooltip": false,
		"separate-outputs": true
	},
	"custom/email": {
		"exec": "sb-mail",
		"interval": 600,
		"signal": 1,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-mail",
		"on-click-middle": "BLOCK_BUTTON=2 sb-mail",
		"on-click-right": "BLOCK_BUTTON=3 sb-mail",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-mail",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-mail"
	},
	"custom/music": {
		"exec": "sb-music",
		"interval": "once",
		"signal": 2,
		"tooltip": false,
		"max-length": 50,
		"on-click": "BLOCK_BUTTON=1 sb-music",
		"on-click-middle": "BLOCK_BUTTON=2 sb-music",
		"on-click-right": "BLOCK_BUTTON=3 sb-music",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-music",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-music"
	},
	"custom/disk": {
		"exec": "sb-disk",
		"interval": 5,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-disk",
		"on-click-middle": "BLOCK_BUTTON=2 sb-disk",
		"on-click-right": "BLOCK_BUTTON=3 sb-disk",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-disk",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-disk"
	},
	"custom/memory": {
		"exec": "sb-memory",
		"interval": 1,
		"signal": 4,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-memory",
		"on-click-middle": "BLOCK_BUTTON=2 sb-memory",
		"on-click-right": "BLOCK_BUTTON=3 sb-memory",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-memory",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-memory"
	},
	"custom/swap": {
		"exec": "sb-swap",
		"interval": 1,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-swap",
		"on-click-middle": "BLOCK_BUTTON=2 sb-swap",
		"on-click-right": "BLOCK_BUTTON=3 sb-swap",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-swap",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-swap"
	},
	"custom/cpu": {
		"exec": "sb-loadavg",
		"interval": 1,
		"signal": 5,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-loadavg",
		"on-click-middle": "BLOCK_BUTTON=2 sb-loadavg",
		"on-click-right": "BLOCK_BUTTON=3 sb-loadavg",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-loadavg",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-loadavg"
	},
	"custom/microphone": {
		"exec": "sb-mic",
		"interval": "once",
		"signal": 6,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-mic",
		"on-click-middle": "BLOCK_BUTTON=2 sb-mic",
		"on-click-right": "BLOCK_BUTTON=3 sb-mic",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-mic",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-mic"
	},
	"custom/screen-recording": {
		"exec": "sb-record",
		"interval": "once",
		"signal": 7,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-record",
		"on-click-middle": "BLOCK_BUTTON=2 sb-record",
		"on-click-right": "BLOCK_BUTTON=3 sb-record",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-record",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-record"
	},
	"custom/audio": {
		"exec": "sb-volume",
		"interval": "once",
		"signal": 8,
		"tooltip": false,
		"smooth-scrolling-threshold": 0.12,
		"on-click": "BLOCK_BUTTON=1 sb-volume",
		"on-click-middle": "BLOCK_BUTTON=2 sb-volume",
		"on-click-right": "BLOCK_BUTTON=3 sb-volume",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-volume",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-volume"
	},
	"custom/battery": {
		"exec": "sb-battery",
		"interval": 5,
		"signal": 9,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-battery",
		"on-click-middle": "BLOCK_BUTTON=2 sb-battery",
		"on-click-right": "BLOCK_BUTTON=3 sb-battery",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-battery",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-battery"
	},
	"custom/date": {
		"exec": "sb-date",
		"interval": 1,
		"signal": 10,
		"tooltip": false,
		"on-click": "BLOCK_BUTTON=1 sb-date",
		"on-click-middle": "BLOCK_BUTTON=2 sb-date",
		"on-click-right": "BLOCK_BUTTON=3 sb-date",
		"on-scroll-up": "BLOCK_BUTTON=4 sb-date",
		"on-scroll-down": "BLOCK_BUTTON=5 sb-date"
	},
	"tray": {
		"icon-size": 16,
		"spacing": 10
	}
}