Commit `8e8c03891a`

8e8c03891a17798067a8da0a034725bf44ece8d0

parent: fe4290fab4

Verified · cmc

cmc <hello@cleberg.net> · 2026-07-15 16:13 UTC

fix: refuse to start when the cache directory is not writable

An unwritable cache directory degraded silently: media still served, because
the download succeeds before the cache write is attempted, so the only symptom
was one "permission denied" line per request and a cache that never filled.
Every request re-fetched from the CDN.

Probe the directory at startup and exit with the uid and the chown that fixes
it. The container image runs as uid 10000, which is the usual cause with a
bind-mounted cache, so say so in the message and in both compose examples.

Layout: unified · split

SETUP.md +4 −1

		@@ -12,7 +12,10 @@ Time units:
12	12	* `uri` — Instance URI. Example: `"uri":"/art/"` -> https://skunky.ebloid.ru/art/
13	13	* `cache` — Caching system; default is off.
14	14	* `enabled` — Caching system state, requires boolean value
15		* `path` — Path to cache directory, requires absolute filesystem path
	15	* `path` — Path to cache directory. It must be writable by the user SkunkyArt
	16	runs as, and SkunkyArt refuses to start if it is not. The container image
	17	runs as uid 10000, so a bind-mounted cache needs
	18	`sudo chown -R 10000:10000 <dir>` on the host.
16	19	* `lifetime` — Cached file life time, requires numeric value, followed by multiplicative suffix (see Time Units for details)
17	20	* `max-size` — Maximum file size in megabytes
18	21	* `update-interval` — Automatic rotation interval

app/config.go +28 −1

		@@ -58,9 +58,28 @@ var CFG = config{
58	58
59	59	var lifetimeParsed int64
60	60
	61	// checkCacheWritable creates the cache directory if it is missing and confirms
	62	// this process can actually write into it, returning the error that a real cache
	63	// write would hit.
	64	//
	65	// An unwritable cache directory is otherwise a silent cliff: every media request
	66	// still succeeds by re-downloading from the CDN, so the only symptom is one
	67	// "permission denied" line per request and a cache that never fills.
	68	func checkCacheWritable(path string) error {
	69	if err := os.MkdirAll(path, 0700); err != nil {
	70	return err
	71	}
	72	probe := path + "/.skunkyart-write-probe"
	73	if err := os.WriteFile(probe, nil, 0600); err != nil {
	74	return err
	75	}
	76	return os.Remove(probe)
	77	}
	78
61	79	// ExecuteConfig loads the config file into CFG, validates it, and starts the
62	80	// cache rotation loop if caching is on. It exits the process on a config that
63		// cannot be read or that asks for caching without proxying.
	81	// cannot be read, that asks for caching without proxying, or that points caching
	82	// at a directory this process cannot write.
64	83	func ExecuteConfig() {
65	84	if CFG.cfg != "" {
66	85	f, err := os.ReadFile(CFG.cfg)
		@@ -71,6 +90,14 @@ func ExecuteConfig() {
71	90	}
72	91
73	92	if CFG.Cache.Enabled {
	93	if err := checkCacheWritable(CFG.Cache.Path); err != nil {
	94	exit("Cache directory is not writable by this process (uid "+
	95	strconv.Itoa(os.Getuid())+"): "+err.Error()+
	96	"\nGrant that uid write access to the directory, or set cache.enabled to false."+
	97	"\nThe official container image runs as uid 10000, so a bind-mounted cache needs:"+
	98	"\n chown -R 10000:10000 <cache dir on the host>", 1)
	99	}
	100
74	101	if CFG.Cache.Lifetime != "" {
75	102	var duration int64
76	103	day := 24 * time.Hour.Milliseconds()

compose.example.yaml +4 −1

		@@ -14,4 +14,7 @@ services:
14	14	- no-new-privileges:true
15	15	volumes:
16	16	- ./config.json:/config.json:ro
17		- ./cache:/cache # Ensure cache folder has a 10000:10000 ownership.
	17	# The image runs as uid 10000, so the host cache dir must be writable by it:
	18	# mkdir -p cache && sudo chown -R 10000:10000 cache
	19	# Without this the container exits at startup telling you the same thing.
	20	- ./cache:/cache

compose.vpn_example.yml +3 −1

		@@ -59,7 +59,9 @@ services:
59	59	- no-new-privileges:true
60	60	volumes:
61	61	- ./config.json:/config.json:ro
62		- ./cache:/cache # ensure this dir is owned 10000:10000
	62	# The image runs as uid 10000, so the host cache dir must be writable by it:
	63	# mkdir -p cache && sudo chown -R 10000:10000 cache
	64	- ./cache:/cache
63	65	environment:
64	66	# Empty by default = direct. Set SKUNKY_PROXY in .env to route via the VPN.
65	67	- HTTPS_PROXY=${SKUNKY_PROXY:-}

Commit 8e8c03891a

Commit `8e8c03891a`