我正在关注docker文档以测试数据卷的备份过程。
以下两个步骤都可以：
docker create -v /dbdata --name dbdata training/postgres /bin/true
docker run -d --volumes-from dbdata --name db1 training/postgres
但是备份数据的输出是：
[root@localhost data]# docker run --volumes-from dbdata -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar /dbdata
tar: /backup/backup.tar: Cannot open: Permission denied
tar: Error is not recoverable: exiting now
[root@localhost data]# pwd
/root/data
[root@localhost data]# ls -alt
total 4
drwxrwxrwx. 2 root root 6 May 7 21:33 .
drwxrwx-w-. 15 root root 4096 May 7 21:33 ..
我以root用户身份工作，为什么会提示“ Permission denied”？
执行调试命令后：
docker run --name ins --volumes-from dbdata -v $(pwd):/backup ubuntu sleep 99999 &
docker inspect ins
输出为：
[{
"AppArmorProfile": "",
"Args": [
"99999"
],
"Config": {
"AttachStderr": true,
"AttachStdin": false,
"AttachStdout": true,
"Cmd": [
"sleep",
"99999"
],
"CpuShares": 0,
"Cpuset": "",
"Domainname": "",
"Entrypoint": null,
"Env": null,
"ExposedPorts": null,
"Hostname": "83e3e1715648",
"Image": "ubuntu",
"MacAddress": "",
"Memory": 0,
"MemorySwap": 0,
"NetworkDisabled": false,
"OnBuild": null,
"OpenStdin": false,
"PortSpecs": null,
"StdinOnce": false,
"Tty": false,
"User": "",
"Volumes": null,
"WorkingDir": ""
},
"Created": "2015-05-08T01:36:35.564512894Z",
"Driver": "devicemapper",
"ExecDriver": "native-0.2",
"ExecIDs": null,
"HostConfig": {
"Binds": [
"/root/data:/backup"
],
"CapAdd": null,
"CapDrop": null,
"ContainerIDFile": "",
"Devices": [],
"Dns": null,
"DnsSearch": null,
"ExtraHosts": null,
"IpcMode": "",
"Links": null,
"LxcConf": [],
"NetworkMode": "bridge",
"PidMode": "",
"PortBindings": {},
"Privileged": false,
"PublishAllPorts": false,
"ReadonlyRootfs": false,
"RestartPolicy": {
"MaximumRetryCount": 0,
"Name": ""
},
"SecurityOpt": null,
"VolumesFrom": [
"dbdata"
]
},
"HostnamePath": "/var/lib/docker/containers/83e3e171564841460b206a8699c1890e2b910bcd2232fdc7202cbff9210b5362/hostname",
"HostsPath": "/var/lib/docker/containers/83e3e171564841460b206a8699c1890e2b910bcd2232fdc7202cbff9210b5362/hosts",
"Id": "83e3e171564841460b206a8699c1890e2b910bcd2232fdc7202cbff9210b5362",
"Image": "07f8e8c5e66084bef8f848877857537ffe1c47edd01a93af27e7161672ad0e95",
"MountLabel": "system_u:object_r:svirt_sandbox_file_t:s0:c414,c650",
"Name": "/ins",
"NetworkSettings": {
"Bridge": "docker0",
"Gateway": "172.17.42.1",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"IPAddress": "172.17.0.6",
"IPPrefixLen": 16,
"IPv6Gateway": "",
"LinkLocalIPv6Address": "fe80::42:acff:fe11:6",
"LinkLocalIPv6PrefixLen": 64,
"MacAddress": "02:42:ac:11:00:06",
"PortMapping": null,
"Ports": {}
},
"Path": "sleep",
"ProcessLabel": "system_u:system_r:svirt_lxc_net_t:s0:c414,c650",
"ResolvConfPath": "/var/lib/docker/containers/83e3e171564841460b206a8699c1890e2b910bcd2232fdc7202cbff9210b5362/resolv.conf",
"RestartCount": 0,
"State": {
"Error": "",
"ExitCode": 0,
"FinishedAt": "0001-01-01T00:00:00Z",
"OOMKilled": false,
"Paused": false,
"Pid": 3614,
"Restarting": false,
"Running": true,
"StartedAt": "2015-05-08T01:36:36.231389015Z"
},
"Volumes": {
"/backup": "/root/data",
"/dbdata": "/var/lib/docker/vfs/dir/df0378f15f61c8f2e220421968fe181cdcf1a03613218c716c81477dda4bdf76"
},
"VolumesRW": {
"/backup": true,
"/dbdata": true
}
}
]
我也尝试以下命令：
[root@localhost data]# docker run --volumes-from dbdata -v $(pwd):/backup -it ubuntu
root@e59c628417f5:/# ls
backup bin boot dbdata dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
root@e59c628417f5:/# ls -alt
total 72
......
drwxrwxrwx. 2 root root 6 May 8 01:33 backup
......
root@e59c628417f5:/# ls -alt backup/
ls: cannot open directory backup/: Permission denied
因此，我认为根本原因仍然在于用户权限。
我只是尝试了您列出的命令，它们在OSX平台和直接Linux平台下都对我有用。问题是您正在将$（pwd）（从主机）挂载到/ backup（在ubuntu映像中，上面运行的第三个docker）。
我怀疑当您启动命令时，您是否位于不可写的目录中？我试图让它失败是这样的：
mkdir failme
chmod 000 failme
cd failme
docker run --volumes-from dbdata -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar /dbdata
但是，它有效:-)
因此，我进入了root不能写的目录：
cd /proc
root@kube:/proc# docker run --volumes-from dbdata -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar /dbdata
tar: /backup/backup.tar: Cannot open: Permission denied
tar: Error is not recoverable: exiting now
您是否可能从无法由root写入的目录开始？
请将输出发布到以下命令：首先，运行：
docker run --name ins --volumes-from dbdata -v $(pwd):/backup ubuntu sleep 99999 &
（而不是您列出的backup command命令。）
然后进行检查并发布这些结果：
docker inspect ins
答案是那是由selinux引起的错误。原始海报找到了答案：
setenforce 0
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我来说两句