为什么 docker 容器中的 shell 显示来自主机的 dmesg 内容？
Why is a shell within a docker container showing dmesg content from the host?
我在 Ubuntu yakkety 上有一个 docker 容器 运行ning Debian jessie。
当在 docker 内（例如通过 ssh 连接）时，我与主机隔离（这是预期的）。然而，我意识到 dmesg 向我显示了主机而不是容器的消息。 它如何访问其主机的信息？
docker容器的配置并不特殊（除了它使用特定的网桥，不同于docker0），特别是它在任何特权模式下都不运行 （下图"Privileged": false）：
root@srv ~# docker inspect minecraft-1-8
[
{
"Id": "748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e",
"Created": "2016-12-01T15:35:05.287672787Z",
"Path": "/usr/bin/supervisord",
"Args": [],
"State": {
"Status": "running",
"Running": true,
"Paused": false,
"Restarting": false,
"OOMKilled": false,
"Dead": false,
"Pid": 28650,
"ExitCode": 0,
"Error": "",
"StartedAt": "2016-12-15T18:37:08.409564695Z",
"FinishedAt": "2016-12-15T18:37:07.457274028Z"
},
"Image": "sha256:78a2f88d47e29523503c2196ed2faaa3d1039d948d73987edc03b2abd338595d",
"ResolvConfPath": "/var/lib/docker/containers/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e/resolv.conf",
"HostnamePath": "/var/lib/docker/containers/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e/hostname",
"HostsPath": "/var/lib/docker/containers/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e/hosts",
"LogPath": "/var/lib/docker/containers/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e-json.log",
"Name": "/minecraft-1-8",
"RestartCount": 0,
"Driver": "overlay",
"MountLabel": "",
"ProcessLabel": "",
"AppArmorProfile": "",
"ExecIDs": null,
"HostConfig": {
"Binds": null,
"ContainerIDFile": "",
"LogConfig": {
"Type": "json-file",
"Config": {}
},
"NetworkMode": "docker",
"PortBindings": {},
"RestartPolicy": {
"Name": "no",
"MaximumRetryCount": 0
},
"AutoRemove": false,
"VolumeDriver": "",
"VolumesFrom": null,
"CapAdd": null,
"CapDrop": null,
"Dns": [],
"DnsOptions": [],
"DnsSearch": [],
"ExtraHosts": null,
"GroupAdd": null,
"IpcMode": "",
"Cgroup": "",
"Links": null,
"OomScoreAdj": 0,
"PidMode": "",
"Privileged": false,
"PublishAllPorts": false,
"ReadonlyRootfs": false,
"SecurityOpt": null,
"UTSMode": "",
"UsernsMode": "",
"ShmSize": 67108864,
"Runtime": "runc",
"ConsoleSize": [
0,
0
],
"Isolation": "",
"CpuShares": 0,
"Memory": 0,
"CgroupParent": "",
"BlkioWeight": 0,
"BlkioWeightDevice": null,
"BlkioDeviceReadBps": null,
"BlkioDeviceWriteBps": null,
"BlkioDeviceReadIOps": null,
"BlkioDeviceWriteIOps": null,
"CpuPeriod": 0,
"CpuQuota": 0,
"CpusetCpus": "",
"CpusetMems": "",
"Devices": [],
"DiskQuota": 0,
"KernelMemory": 0,
"MemoryReservation": 0,
"MemorySwap": 0,
"MemorySwappiness": -1,
"OomKillDisable": false,
"PidsLimit": 0,
"Ulimits": null,
"CpuCount": 0,
"CpuPercent": 0,
"IOMaximumIOps": 0,
"IOMaximumBandwidth": 0
},
"GraphDriver": {
"Name": "overlay",
"Data": {
"LowerDir": "/var/lib/docker/overlay/e78ce9dbcedd6974429a4aada8f38913b7d35da41f586f203dd99a568f38b6c3/root",
"MergedDir": "/var/lib/docker/overlay/e8422e4707d95db8ea747af2367626cc8bf16e95f8eb05dfad9a63461c9ade86/merged",
"UpperDir": "/var/lib/docker/overlay/e8422e4707d95db8ea747af2367626cc8bf16e95f8eb05dfad9a63461c9ade86/upper",
"WorkDir": "/var/lib/docker/overlay/e8422e4707d95db8ea747af2367626cc8bf16e95f8eb05dfad9a63461c9ade86/work"
}
},
"Mounts": [],
"Config": {
"Hostname": "minecraft-1-8",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": true,
"AttachStderr": true,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/usr/bin/supervisord"
],
"Image": "minecraft",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {}
},
"NetworkSettings": {
"Bridge": "",
"SandboxID": "cf411634babad31138ab4572b9cd7306f74a54dd1baf4cd8d7706d7e7020c594",
"HairpinMode": false,
"LinkLocalIPv6Address": "",
"LinkLocalIPv6PrefixLen": 0,
"Ports": {},
"SandboxKey": "/var/run/docker/netns/cf411634baba",
"SecondaryIPAddresses": null,
"SecondaryIPv6Addresses": null,
"EndpointID": "",
"Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"IPAddress": "",
"IPPrefixLen": 0,
"IPv6Gateway": "",
"MacAddress": "",
"Networks": {
"docker": {
"IPAMConfig": {
"IPv4Address": "10.200.0.100"
},
"Links": null,
"Aliases": [
"748cfdfbf3fb"
],
"NetworkID": "7b20560b36032d36ffe6c0ebece6b4408355d207f4e203a2957b0434ee0afdc1",
"EndpointID": "9fa4fc914dfe76022ce0db02e48a7e7c85c57bc2a15b0b3e5d81b1f24d95f376",
"Gateway": "10.200.0.1",
"IPAddress": "10.200.0.100",
"IPPrefixLen": 24,
"IPv6Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"MacAddress": "02:42:0a:c8:00:64"
}
}
}
}
]
在大多数发行版的 dmesg is not a privileged command. Any user can use the klogctl 接口中读取内核环形缓冲区。
$ id
uid=1001(matt) gid=1001(matt) groups=1001(matt)
$ dmesg | head -1
[ 0.000000] Initializing cgroup subsys cpuset
但除了读取之外什么也做不了
$ dmesg -C
dmesg: klogctl failed: Operation not permitted
延伸至 Docker
$ sudo docker run debian dmesg | head -1
[ 0.000000] Initializing cgroup subsys cpuset
$ sudo docker run debian dmesg -C
dmesg: klogctl failed: Operation not permitted
限制访问
您可以通过 /proc/sys/kernel/dmesg_restrict 将读取权限限制为 root 用户和具有 CAP_SYSLOG 或 CAP_SYS_ADMIN capabilities 的用户。
$ echo 1 > /proc/sys/kernel/dmesg_restrict
那么您应该会收到一条权限被拒绝的消息：
$ docker run ubuntu:yakkety dmesg
dmesg: read kernel buffer failed: Operation not permitted
运行 特权模式下的容器将重新获得对主机内核环缓冲区的访问权限
$ docker run --privileged ubuntu:yakkety dmesg
[146902.131915] br-fa26f1dc96a1: port 3(veth80d3d5d) entered disabled state
...
如果您永久需要它，请使用 sysctl 配置 kernel.dmesg_restrict=1。
命名空间
至于为什么内核日志不像其他内核区域那样有名称间距，我认为答案是"it's difficult"。在这个 2012 Stepping closer to practical containers: "syslog" namespaces LWN post. I can't see any reference's to it getting any further than proposed patches: https://lwn.net/Articles/562389/ https://lwn.net/Articles/561271/. As you can see in this recent netfilter patch 中，有比你想知道的更多的细节，他们有一个变通方法允许容器名称 space 中的规则使用全局日志。
我在 Ubuntu yakkety 上有一个 docker 容器 运行ning Debian jessie。
当在 docker 内（例如通过 ssh 连接）时，我与主机隔离（这是预期的）。然而，我意识到 dmesg 向我显示了主机而不是容器的消息。 它如何访问其主机的信息？
docker容器的配置并不特殊（除了它使用特定的网桥，不同于docker0），特别是它在任何特权模式下都不运行 （下图"Privileged": false）：
root@srv ~# docker inspect minecraft-1-8
[
{
"Id": "748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e",
"Created": "2016-12-01T15:35:05.287672787Z",
"Path": "/usr/bin/supervisord",
"Args": [],
"State": {
"Status": "running",
"Running": true,
"Paused": false,
"Restarting": false,
"OOMKilled": false,
"Dead": false,
"Pid": 28650,
"ExitCode": 0,
"Error": "",
"StartedAt": "2016-12-15T18:37:08.409564695Z",
"FinishedAt": "2016-12-15T18:37:07.457274028Z"
},
"Image": "sha256:78a2f88d47e29523503c2196ed2faaa3d1039d948d73987edc03b2abd338595d",
"ResolvConfPath": "/var/lib/docker/containers/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e/resolv.conf",
"HostnamePath": "/var/lib/docker/containers/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e/hostname",
"HostsPath": "/var/lib/docker/containers/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e/hosts",
"LogPath": "/var/lib/docker/containers/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e/748cfdfbf3fb5526cb7151cbc0857117af3c7bd8ab9e086c4f2efb897290d66e-json.log",
"Name": "/minecraft-1-8",
"RestartCount": 0,
"Driver": "overlay",
"MountLabel": "",
"ProcessLabel": "",
"AppArmorProfile": "",
"ExecIDs": null,
"HostConfig": {
"Binds": null,
"ContainerIDFile": "",
"LogConfig": {
"Type": "json-file",
"Config": {}
},
"NetworkMode": "docker",
"PortBindings": {},
"RestartPolicy": {
"Name": "no",
"MaximumRetryCount": 0
},
"AutoRemove": false,
"VolumeDriver": "",
"VolumesFrom": null,
"CapAdd": null,
"CapDrop": null,
"Dns": [],
"DnsOptions": [],
"DnsSearch": [],
"ExtraHosts": null,
"GroupAdd": null,
"IpcMode": "",
"Cgroup": "",
"Links": null,
"OomScoreAdj": 0,
"PidMode": "",
"Privileged": false,
"PublishAllPorts": false,
"ReadonlyRootfs": false,
"SecurityOpt": null,
"UTSMode": "",
"UsernsMode": "",
"ShmSize": 67108864,
"Runtime": "runc",
"ConsoleSize": [
0,
0
],
"Isolation": "",
"CpuShares": 0,
"Memory": 0,
"CgroupParent": "",
"BlkioWeight": 0,
"BlkioWeightDevice": null,
"BlkioDeviceReadBps": null,
"BlkioDeviceWriteBps": null,
"BlkioDeviceReadIOps": null,
"BlkioDeviceWriteIOps": null,
"CpuPeriod": 0,
"CpuQuota": 0,
"CpusetCpus": "",
"CpusetMems": "",
"Devices": [],
"DiskQuota": 0,
"KernelMemory": 0,
"MemoryReservation": 0,
"MemorySwap": 0,
"MemorySwappiness": -1,
"OomKillDisable": false,
"PidsLimit": 0,
"Ulimits": null,
"CpuCount": 0,
"CpuPercent": 0,
"IOMaximumIOps": 0,
"IOMaximumBandwidth": 0
},
"GraphDriver": {
"Name": "overlay",
"Data": {
"LowerDir": "/var/lib/docker/overlay/e78ce9dbcedd6974429a4aada8f38913b7d35da41f586f203dd99a568f38b6c3/root",
"MergedDir": "/var/lib/docker/overlay/e8422e4707d95db8ea747af2367626cc8bf16e95f8eb05dfad9a63461c9ade86/merged",
"UpperDir": "/var/lib/docker/overlay/e8422e4707d95db8ea747af2367626cc8bf16e95f8eb05dfad9a63461c9ade86/upper",
"WorkDir": "/var/lib/docker/overlay/e8422e4707d95db8ea747af2367626cc8bf16e95f8eb05dfad9a63461c9ade86/work"
}
},
"Mounts": [],
"Config": {
"Hostname": "minecraft-1-8",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": true,
"AttachStderr": true,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/usr/bin/supervisord"
],
"Image": "minecraft",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {}
},
"NetworkSettings": {
"Bridge": "",
"SandboxID": "cf411634babad31138ab4572b9cd7306f74a54dd1baf4cd8d7706d7e7020c594",
"HairpinMode": false,
"LinkLocalIPv6Address": "",
"LinkLocalIPv6PrefixLen": 0,
"Ports": {},
"SandboxKey": "/var/run/docker/netns/cf411634baba",
"SecondaryIPAddresses": null,
"SecondaryIPv6Addresses": null,
"EndpointID": "",
"Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"IPAddress": "",
"IPPrefixLen": 0,
"IPv6Gateway": "",
"MacAddress": "",
"Networks": {
"docker": {
"IPAMConfig": {
"IPv4Address": "10.200.0.100"
},
"Links": null,
"Aliases": [
"748cfdfbf3fb"
],
"NetworkID": "7b20560b36032d36ffe6c0ebece6b4408355d207f4e203a2957b0434ee0afdc1",
"EndpointID": "9fa4fc914dfe76022ce0db02e48a7e7c85c57bc2a15b0b3e5d81b1f24d95f376",
"Gateway": "10.200.0.1",
"IPAddress": "10.200.0.100",
"IPPrefixLen": 24,
"IPv6Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"MacAddress": "02:42:0a:c8:00:64"
}
}
}
}
]
在大多数发行版的 dmesg is not a privileged command. Any user can use the klogctl 接口中读取内核环形缓冲区。
$ id
uid=1001(matt) gid=1001(matt) groups=1001(matt)
$ dmesg | head -1
[ 0.000000] Initializing cgroup subsys cpuset
但除了读取之外什么也做不了
$ dmesg -C
dmesg: klogctl failed: Operation not permitted
延伸至 Docker
$ sudo docker run debian dmesg | head -1
[ 0.000000] Initializing cgroup subsys cpuset
$ sudo docker run debian dmesg -C
dmesg: klogctl failed: Operation not permitted
限制访问
您可以通过 /proc/sys/kernel/dmesg_restrict 将读取权限限制为 root 用户和具有 CAP_SYSLOG 或 CAP_SYS_ADMIN capabilities 的用户。
$ echo 1 > /proc/sys/kernel/dmesg_restrict
那么您应该会收到一条权限被拒绝的消息：
$ docker run ubuntu:yakkety dmesg
dmesg: read kernel buffer failed: Operation not permitted
运行 特权模式下的容器将重新获得对主机内核环缓冲区的访问权限
$ docker run --privileged ubuntu:yakkety dmesg
[146902.131915] br-fa26f1dc96a1: port 3(veth80d3d5d) entered disabled state
...
如果您永久需要它，请使用 sysctl 配置 kernel.dmesg_restrict=1。
命名空间
至于为什么内核日志不像其他内核区域那样有名称间距，我认为答案是"it's difficult"。在这个 2012 Stepping closer to practical containers: "syslog" namespaces LWN post. I can't see any reference's to it getting any further than proposed patches: https://lwn.net/Articles/562389/ https://lwn.net/Articles/561271/. As you can see in this recent netfilter patch 中，有比你想知道的更多的细节，他们有一个变通方法允许容器名称 space 中的规则使用全局日志。