aghnet: do not expect dhcpdc.conf to exist

CHANGELOG.md

@@ -47,6 +47,7 @@ released by then.
 
 ### Fixed
 
+- Errors when setting static IP on Linux ([#3257]).
 - Treatment of domain names and FQDNs in custom rules with `$dnsrewrite` that
   use the `PTR` type ([#3256]).
 - Redundant hostname generating while loading static leases with empty hostname
@@ -73,6 +74,7 @@ released by then.
 [#3194]: https://github.com/AdguardTeam/AdGuardHome/issues/3194
 [#3198]: https://github.com/AdguardTeam/AdGuardHome/issues/3198
 [#3256]: https://github.com/AdguardTeam/AdGuardHome/issues/3256
+[#3257]: https://github.com/AdguardTeam/AdGuardHome/issues/3257
 
 
 

internal/aghnet/net_linux.go

@@ -138,10 +138,10 @@ func ifaceSetStaticIP(ifaceName string) (err error) {
 	}
 
 	gatewayIP := GatewayIP(ifaceName)
-	add := updateStaticIPdhcpcdConf(ifaceName, ipNet.String(), gatewayIP, ipNet.IP)
+	add := updateStaticIPDhcpcdConf(ifaceName, ipNet.String(), gatewayIP, ipNet.IP)
 
 	body, err := os.ReadFile("/etc/dhcpcd.conf")
-	if err != nil {
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
 		return err
 	}
 
@@ -154,23 +154,23 @@ func ifaceSetStaticIP(ifaceName string) (err error) {
 	return nil
 }
 
-// updateStaticIPdhcpcdConf sets static IP address for the interface by writing
-// into dhcpd.conf.
-func updateStaticIPdhcpcdConf(ifaceName, ip string, gatewayIP, dnsIP net.IP) string {
+// updateStaticIPDhcpcdConf sets static IP address for the interface by writing
+// into dhcpdc.conf.
+func updateStaticIPDhcpcdConf(ifaceName, ip string, gatewayIP, dnsIP net.IP) string {
 	var body []byte
 
-	add := fmt.Sprintf("\ninterface %s\nstatic ip_address=%s\n",
-		ifaceName, ip)
+	add := fmt.Sprintf(
+		"\n# %[1]s added by AdGuard Home.\ninterface %[1]s\nstatic ip_address=%s\n",
+		ifaceName,
+		ip)
 	body = append(body, []byte(add)...)
 
 	if gatewayIP != nil {
-		add = fmt.Sprintf("static routers=%s\n",
-			gatewayIP)
+		add = fmt.Sprintf("static routers=%s\n", gatewayIP)
 		body = append(body, []byte(add)...)
 	}
 
-	add = fmt.Sprintf("static domain_name_servers=%s\n\n",
-		dnsIP)
+	add = fmt.Sprintf("static domain_name_servers=%s\n\n", dnsIP)
 	body = append(body, []byte(add)...)
 
 	return string(body)

internal/aghnet/net_linux_test.go

@@ -103,22 +103,24 @@ func TestSetStaticIPdhcpcdConf(t *testing.T) {
 		routers    net.IP
 	}{{
 		name: "with_gateway",
-		dhcpcdConf: nl + `interface wlan0` + nl +
+		dhcpcdConf: nl + `# wlan0 added by AdGuard Home.` + nl +
+			`interface wlan0` + nl +
 			`static ip_address=192.168.0.2/24` + nl +
 			`static routers=192.168.0.1` + nl +
 			`static domain_name_servers=192.168.0.2` + nl + nl,
 		routers: net.IP{192, 168, 0, 1},
 	}, {
 		name: "without_gateway",
-		dhcpcdConf: nl + `interface wlan0` + nl +
+		dhcpcdConf: nl + `# wlan0 added by AdGuard Home.` + nl +
+			`interface wlan0` + nl +
 			`static ip_address=192.168.0.2/24` + nl +
 			`static domain_name_servers=192.168.0.2` + nl + nl,
 		routers: nil,
 	}}
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			s := updateStaticIPdhcpcdConf("wlan0", "192.168.0.2/24", tc.routers, net.IP{192, 168, 0, 2})
+			s := updateStaticIPDhcpcdConf("wlan0", "192.168.0.2/24", tc.routers, net.IP{192, 168, 0, 2})
 			assert.Equal(t, tc.dhcpcdConf, s)
 		})
 	}