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修复docker pull image failed

docker pull报错

message":"Get https://n6-026-137.byted.org/v1/_ping: Not Found"},"error":"Get https://n6-026-137.byted.org/v1/_ping: Not Found

排查

打开docker的调试开关，给dockerd的启动参数中加入-D参数：

vi /lib/systemd/system/docker.service
ExecStart=/usr/bin/dockerd -D -H unix:///var/run/docker.sock -g="/opt/docker"

dockerd 的日志（docker pull/push的日志）会记录到/var/log/daemon.log中，再次触发错误之后，在daemon.log中没有找到更多有用的信息：

Dec 1 17:12:13 n6-026-137 dockerd[138149]: time="2016-12-01T17:12:13.537485265+08:00" level=error msg="Attempting next endpoint for push after error: Get https://sandbox.hub.byted.org/v1/_ping : Not Found"

因为这个是测试服务器，dockerd上通过的信息并不多，直接strace docker的进程，找到出错的原因：

ERR_DNS_FAIL

strace -ff -s256 -p 138149 2>&1 |awk '{print $0}' > a.out
[pid 191579] <... read resumed> "HTTP/1.0 404 Not Found/r/nServer: squid/3.1.20/r/nMime-Version: 1.0/r/nDate: Thu, 01 Dec
    2016 09:14:36 GMT/r/nContent-Type: text/html/r/nContent-Length: 3281/r/nX-Squid-Error: ERR_DNS_FAIL 0/r/nVary: Accept-Lang
    uage/r/nContent-Language: en/r/n/r/n<!DOCTYPE html PUBLIC /"-//W3C"..., 4096) = 3508