关于 Ubuntu 上时不时 SSID 消失的问题
久仰这个 bug 啊，自从李先生吃上了 Ubuntu 16.04 之后我就听闻了这个 bug，在 suspend 几次之后就会出现 SSID 扫不到的事。入职这边之后的确接触了很长时间 Ubuntu，然后碰到了这个 bug，复现率不算特别高，但是也经常出现烦人。偶尔逮到一次，于是来看看到底是怎么回事。
首先只能看到的是 SSID 扫不到了，先看看 NetworkManager 的状态，是 active 的，那问题不在 NetworkManager 这里。
那难道是驱动嗝屁了？用 dmesg 搜索了一下驱动相关的信息，倒是有报错，我最新的 firmware 是21的，跟我要22和23的，我就顺势装上了23和24的，过了一会再看，跟我要25和26的……那看来不是驱动的问题……
别人问了一句说用 iwlist scan 能不能扫出 SSID 呢，我试了一下，是不能的，这倒是提醒了我，NetworkManager 一般是读 wpasupplicant 提供的结果，那我用 wpa_cli 来扫扫看，然后发现 wpa_cli 连不上 wpasupplicant，ps 看了一眼，wpasupplicant 根本没起来，那自然扫不到 SSID 咯，问题找到。用 systemctl 看看 wpasupplicant 到底咋了。
● wpa_supplicant.service - WPA supplicant Loaded: loaded (/lib/systemd/system/wpa_supplicant.service; disabled; vendor preset: enabled) Active: inactive (dead) Dec 12 04:14:11 ubuntu-desktop wpa_supplicant[2882]: Successfully initialized wpa_supplicant Dec 12 04:14:11 ubuntu-desktop systemd[1]: Started WPA supplicant. Dec 12 04:14:11 ubuntu-desktop wpa_supplicant[2882]: dbus: wpa_dbus_get_object_properties: failed to get object properties: (none) none Dec 12 04:14:11 ubuntu-desktop wpa_supplicant[2882]: dbus: Failed to construct signal Dec 12 04:14:11 ubuntu-desktop wpa_supplicant[2882]: Could not read interface p2p-dev-wlp4s0 flags: No such device Dec 12 04:15:56 u systemd[1]: Stopping WPA supplicant... Dec 12 04:15:56 u wpa_supplicant[2882]: nl80211: deinit ifname=p2p-dev-wlp4s0 disabled_11b_rates=0 Dec 12 04:15:56 u wpa_supplicant[2882]: p2p-dev-wlp4s0: CTRL-EVENT-TERMINATING Dec 12 04:15:56 u wpa_supplicant[2882]: nl80211: deinit ifname=wlp4s0 disabled_11b_rates=0 Dec 12 04:15:56 u systemd[1]: Stopped WPA supplicant.
可以很清楚地看到有这样一句
Could not read interface p2p-dev-wlp4s0 flags: No such device
看来就是这个问题了，以这句为关键字搜索了一下，看到 Arch 的 BBS 上在15年4月就有讨论的帖子，读了一下，是 wpasupplicant 从2.3升级到2.4的时候引入了一个关于 p2p interface 的 patch，wpasupplicant 不能很好地处理这个问题，所以就时不时嗝屁了。继续翻了一下 Arch 那边的 bug 追踪，他们在 wpasupplicant 2.5 的时候修复了这个问题。我翻了一下 Ubuntu 这边的源，16.04 上还是 2.4，16.10 上也应该是 2.4（如果我找对的话）。
问题是找到了，就看修不修咯╮(￣▽￣)╭
问题的暂时解决办法放最后，其实能看懂的已经知道解决办法了，只要触发重启 wpasupplicant 即可。
$ sudo systemctl restart wpa_supplicant $ sudo systemctl restart NetworkManager
或者干脆重启机器╮(￣▽￣)╭
Dec 14, 2016 10:23:35 AM
原来是这个问题啊……我遇到过一次，然后系统更新了～
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