docker联合文件系统（UnionFS）
学习docker你可能有一下几个疑惑
- 又镜像生成的容器之间到底有什么关系呢
…
带着疑惑请往下看，本篇将解密一切
一个容器到底是由镜像怎么生成的，同一个镜像多个容器之间的文件有什么关联开始你的表演
第一、验证一下，同一个镜像创建多个容器，观察下磁盘的大小是否变化
[root@localhost ~]# docker pull nginx #拉取一个nginx镜像
Using default tag: latest
latest: Pulling from library/nginx
a076a628af6f: Pull complete
0732ab25fa22: Pull complete
d7f36f6fe38f: Pull complete
f72584a26f32: Pull complete
7125e4df9063: Pull complete
Digest: sha256:10b8cc432d56da8b61b070f4c7d2543a9ed17c2b23010b43af434fd40e2ca4aa
Status: Downloaded newer image for nginx:latest
docker.io/library/nginx:latest
[root@localhost ~]# docker images #可以看到当前有一个nginx的镜像
REPOSITORY TAG IMAGE ID CREATED SIZE
nginx latest f6d0b4767a6c 7 weeks ago 133MB #可以看到这个镜像有133M
[root@localhost ~]# df -h
文件系统 容量 已用 可用 已用% 挂载点
/dev/mapper/centos-root 17G 2.0G 15G 12% /
devtmpfs 476M 0 476M 0% /dev
tmpfs 488M 0 488M 0% /dev/shm
tmpfs 488M 7.7M 480M 2% /run
tmpfs 488M 0 488M 0% /sys/fs/cgroup
/dev/sda1 1014M 130M 885M 13% /boot
tmpfs 98M 0 98M 0% /run/user/0
#接下来我们启动more more多的容器看看
[root@localhost ~]# docker run -d nginx
6f3e3f11e0a4d248c9c578608ed1027a714c5190547b4d18a7674caffcd53a79
[root@localhost ~]# docker run -d nginx
e5e18a18ae4b31bc797d28a6542a7687935e1137da8887c3f7270886f521734d
^[[A[root@localhost ~]# docker run -d nginx
7001daddfbdfd879bdbaf5b31f669e60a1952167c99c649d9d24a8799dddfe12
^[[A[root@localhost ~]# docker run -d nginx
6c1f7b3e03933238fa1f3ddb06acb74f85f5325d359e047fdf884711caeab3d8
[root@localhost ~]# docker run -d nginx
dbf9b9fe043e4a1f209570dd4792d375ceaabd1c22d99395d5adbcee307076d8
[root@localhost ~]# docker run -d nginx
433ce7a40a12fafcf03d913ad757ce20e1d78d9dc777a98ca4df84710a09c67f
[root@localhost ~]# docker run -d nginx
ce2693bbb5ad9fdb6e976fcaa4919f526030b4ecdc09528640bda9d73afa123d
[root@localhost ~]# docker run -d nginx
d6f7ef40c825403795d6ece4a9a25f3158ee43a6ac18fc35ada1f77938ad9824
[root@localhost ~]# docker run -d nginx
08de3c93f339d249f95a6e427430c633320cdaff4e31e35447ec5bf284343f61
[root@localhost ~]# docker run -d nginx
4bc994d253ac82d27d15d9db9732d8576ed52e54be468cf316fdeaf7a12ccb63
[root@localhost ~]# docker run -d nginx
e0149592d0516092879805fbd5198bfd49f85f5ce0842981927c1f5c928d3abe
[root@localhost ~]# docker run -d nginx
378ccf0c81a809b5e1ba1d6baa34e27359c672c297caf9e5fea2989cfc4b0dc6
[root@localhost ~]# docker run -d nginx
18afe1e59f03508d2d1b1f163b893a3deea54a838f9dd3f8c2a5e7128cd65bfb
[root@localhost ~]# docker run -d nginx
1c45086a73f9572ed467982a44c5865f883734936783801fe5164af8fe0d6487
[root@localhost ~]# docker ps -a #看到有好多的容器在运行中
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
1c45086a73f9 nginx "/docker-entrypoint.…" 9 seconds ago Up 8 seconds 80/tcp eloquent_gates
18afe1e59f03 nginx "/docker-entrypoint.…" 10 seconds ago Up 9 seconds 80/tcp stupefied_payne
378ccf0c81a8 nginx "/docker-entrypoint.…" 11 seconds ago Up 11 seconds 80/tcp quizzical_cartwright
e0149592d051 nginx "/docker-entrypoint.…" 12 seconds ago Up 12 seconds 80/tcp recursing_almeida
4bc994d253ac nginx "/docker-entrypoint.…" 14 seconds ago Up 13 seconds 80/tcp affectionate_margulis
08de3c93f339 nginx "/docker-entrypoint.…" 15 seconds ago Up 14 seconds 80/tcp naughty_solomon
d6f7ef40c825 nginx "/docker-entrypoint.…" 16 seconds ago Up 15 seconds 80/tcp nifty_proskuriakova
ce2693bbb5ad nginx "/docker-entrypoint.…" 17 seconds ago Up 16 seconds 80/tcp magical_panini
433ce7a40a12 nginx "/docker-entrypoint.…" 19 seconds ago Up 18 seconds 80/tcp intelligent_montalcini
dbf9b9fe043e nginx "/docker-entrypoint.…" 20 seconds ago Up 19 seconds 80/tcp nifty_visvesvaraya
6c1f7b3e0393 nginx "/docker-entrypoint.…" 21 seconds ago Up 20 seconds 80/tcp cranky_mirzakhani
7001daddfbdf nginx "/docker-entrypoint.…" 22 seconds ago Up 21 seconds 80/tcp bold_heisenberg
e5e18a18ae4b nginx "/docker-entrypoint.…" 23 seconds ago Up 22 seconds 80/tcp lucid_banzai
6f3e3f11e0a4 nginx "/docker-entrypoint.…" 27 seconds ago Up 25 seconds 80/tcp recursing_brown
[root@localhost ~]# df -h #可以看到系统磁盘大小还是15G
文件系统 容量 已用 可用 已用% 挂载点
/dev/mapper/centos-root 17G 2.0G 15G 12% /
devtmpfs 476M 0 476M 0% /dev
tmpfs 488M 0 488M 0% /dev/shm
tmpfs 488M 8.6M 479M 2% /run
tmpfs 488M 0 488M 0% /sys/fs/cgroup
/dev/sda1 1014M 130M 885M 13% /boot ###大家要记住下面的这些东西，一会你们聚会恍然大明白了
tmpfs 98M 0 98M 0% /run/user/0
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/b2d0837433350e7454b4e0915127900fc04de1535a9af83404ce94c060df1a54/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/0a8e70f1dc817e574bf3bfccca8ded0f7ceb0a856aff6b259038ebf69649cc66/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/162d59345ca6b4867e2572a1763825952a6212fbc114aad17f4cdfd71191262c/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/4979f6e401872c59a4744558b05f8f86c51bf73cba3e632802ac05c2ce9dceee/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/5e78ced6812cb269b5cc4b3ac9c03a60d2b6cba3edcfb98908971b4996edacd0/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/3a07c83675080b755f662dd181e2062de7142f653eb23cbed312b4fdea78115d/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/f9ffcc3d3a41c9fce77ffc8c5d46b73fd381ac8e3f9fb2352fd6d2c121a892a2/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/3111318b0b752d2500443263cb9576078d934a473ddab78b2c0faf1d2f039f57/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/bd0b83f999d2f17527b9812f608c54a63b5fe3f6df6869b6cc386a38d6058c91/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/503ac746b9f64bb750f953a09282ac146a2a1329caadad36fb846e2ddb564534/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/423f6191634174850ddd91ecbb3cce3fad6245f8ace09d8ec84a66e3a5ed9258/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/dbb5c551bf81d3ea91d39504d4cd53016ff5f699202f0576a1b6ce8a7c513d99/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/1b4d82471b99662962adeb0892f8708da7840d775fd6dfc37a118b7c11f05af9/merged
overlay 17G 2.0G 15G 12% /var/lib/docker/overlay2/080e4cbbcc4082cbe07ae6d5c22f63b0bd9e8caada21d46783097983747c2e34/merged
[root@localhost ~]#
事实证明，有一个镜像创建的多个容器不会对服务器磁盘有太大的影响第二、解剖docker。了解docker内部的世界
[root@localhost ~]# docker ps -aq | xargs docker stop | xargs docker rm ##借助两个管道符先将容器清理一下
1c45086a73f9
18afe1e59f03
378ccf0c81a8
e0149592d051
4bc994d253ac
08de3c93f339
d6f7ef40c825
ce2693bbb5ad
433ce7a40a12
dbf9b9fe043e
6c1f7b3e0393
7001daddfbdf
e5e18a18ae4b
6f3e3f11e0a4
[root@localhost ~]# docker ps -a #可以看到没有容器了
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
##接下来我们创建两个测试容器，分别是web1和web2方便区分
[root@localhost ~]# docker run -d --name=web1 nginx #创建web1容器
afb553ce70c8ac196a810ea1516a866704285cdb7052d9921d197b8f869af9ba
[root@localhost ~]# docker run -d --name=web2 nginx #创建web2容器
be9a8ab117d1386e9ebf67464a039388ca679e304eb00c32b33b15d50a2268be
[root@localhost ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
be9a8ab117d1 nginx "/docker-entrypoint.…" 25 seconds ago Up 24 seconds 80/tcp web2
afb553ce70c8 nginx "/docker-entrypoint.…" 30 seconds ago Up 29 seconds 80/tcp web1
##然后分别在这两个容器里面创建几个文件或目录
[root@localhost ~]# docker exec -it afb553ce70c8 bash
root@afb553ce70c8:/# ls
bin dev docker-entrypoint.sh home lib64 mnt proc run srv tmp var
boot docker-entrypoint.d etc lib media opt root sbin sys usr
root@afb553ce70c8:/# mkdir a aa aaa
root@afb553ce70c8:/# touch a.txt aa.txt aaa.txt
root@afb553ce70c8:/# ls
a aa aaa bin dev docker-entrypoint.sh home lib64 mnt proc run srv tmp var
a.txt aa.txt aaa.txt boot docker-entrypoint.d etc lib media opt root sbin sys usr
root@afb553ce70c8:/# exit
exit
[root@localhost ~]# docker exec -it be9a8ab117d1 bash
root@be9a8ab117d1:/# mkdir b bb bbb
root@be9a8ab117d1:/# touch b.txt bb.txt bbb.txt
root@be9a8ab117d1:/# ls
b bb bbb bin dev docker-entrypoint.sh home lib64 mnt proc run srv tmp var
b.txt bb.txt bbb.txt boot docker-entrypoint.d etc lib media opt root sbin sys usr
root@be9a8ab117d1:/# exit
exit
##创建完成之后，让我们来看看这两个容器的详细信息
[root@localhost ~]# docker inspect web1 | egrep -i data -A 20 -B 1 #web1的目录使用详情
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa-init/diff:/var/lib/docker/overlay2/9ea913b7611a03e5e6ff79e4ad5966323ddc8d22930fd538b8f4d0cbd8adc6ad/diff:/var/lib/docker/overlay2/4ce0979bb143d9e44e3bab1a8827aec82af2124490824dcd0eded2bdea025543/diff:/var/lib/docker/overlay2/727f637b61409b8760394186a49582dc1bc497a0433074b26fdba053d6263d2b/diff:/var/lib/docker/overlay2/5dbf8694ae45b3211108042719d6ecee8a2aa2c6f59db2e9c7d8a374b5e7e804/diff:/var/lib/docker/overlay2/db778a93aefbc70fd58665217197361951cd31f7edf7a89b1e6f222d9a5e85d6/diff",
"MergedDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/merged",
"UpperDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/diff",
"WorkDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/work"
},
"Name": "overlay2"
},
"Mounts": [],
"Config": {
"Hostname": "afb553ce70c8",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"80/tcp": {}
},
"Tty": false,
"OpenStdin": false,
[root@localhost ~]# docker inspect web2 | egrep -i data -A 20 -B 1 #web2目录的使用详情
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459-init/diff:/var/lib/docker/overlay2/9ea913b7611a03e5e6ff79e4ad5966323ddc8d22930fd538b8f4d0cbd8adc6ad/diff:/var/lib/docker/overlay2/4ce0979bb143d9e44e3bab1a8827aec82af2124490824dcd0eded2bdea025543/diff:/var/lib/docker/overlay2/727f637b61409b8760394186a49582dc1bc497a0433074b26fdba053d6263d2b/diff:/var/lib/docker/overlay2/5dbf8694ae45b3211108042719d6ecee8a2aa2c6f59db2e9c7d8a374b5e7e804/diff:/var/lib/docker/overlay2/db778a93aefbc70fd58665217197361951cd31f7edf7a89b1e6f222d9a5e85d6/diff",
"MergedDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/merged",
"UpperDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/diff",
"WorkDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/work"
},
"Name": "overlay2"
},
"Mounts": [],
"Config": {
"Hostname": "be9a8ab117d1",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"80/tcp": {}
},
"Tty": false,
"OpenStdin": false,开始对比这两个容器所用目录的差别
[root@localhost ~]# docker inspect web1 | egrep -i data -A 20 -B 1 > web1.txt
[root@localhost ~]# docker inspect web2 | egrep -i data -A 20 -B 1 > web2.txt
[root@localhost ~]# which diff
/usr/bin/diff
[root@localhost ~]# diff -c web1.txt web2.txt
*** web1.txt 2021-03-04 23:48:36.974208148 +0800
--- web2.txt 2021-03-04 23:48:45.002225087 +0800
***************
*** 1,15 ****
"GraphDriver": {
"Data": {
! "LowerDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa-init/diff:/var/lib/docker/overlay2/9ea913b7611a03e5e6ff79e4ad5966323ddc8d22930fd538b8f4d0cbd8adc6ad/diff:/var/lib/docker/overlay2/4ce0979bb143d9e44e3bab1a8827aec82af2124490824dcd0eded2bdea025543/diff:/var/lib/docker/overlay2/727f637b61409b8760394186a49582dc1bc497a0433074b26fdba053d6263d2b/diff:/var/lib/docker/overlay2/5dbf8694ae45b3211108042719d6ecee8a2aa2c6f59db2e9c7d8a374b5e7e804/diff:/var/lib/docker/overlay2/db778a93aefbc70fd58665217197361951cd31f7edf7a89b1e6f222d9a5e85d6/diff",
! "MergedDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/merged",
! "UpperDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/diff",
! "WorkDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/work"
},
"Name": "overlay2"
},
"Mounts": [],
"Config": {
! "Hostname": "afb553ce70c8",
"Domainname": "",
"User": "",
"AttachStdin": false,
--- 1,15 ----
"GraphDriver": {
"Data": {
! "LowerDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459-init/diff:/var/lib/docker/overlay2/9ea913b7611a03e5e6ff79e4ad5966323ddc8d22930fd538b8f4d0cbd8adc6ad/diff:/var/lib/docker/overlay2/4ce0979bb143d9e44e3bab1a8827aec82af2124490824dcd0eded2bdea025543/diff:/var/lib/docker/overlay2/727f637b61409b8760394186a49582dc1bc497a0433074b26fdba053d6263d2b/diff:/var/lib/docker/overlay2/5dbf8694ae45b3211108042719d6ecee8a2aa2c6f59db2e9c7d8a374b5e7e804/diff:/var/lib/docker/overlay2/db778a93aefbc70fd58665217197361951cd31f7edf7a89b1e6f222d9a5e85d6/diff",
! "MergedDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/merged",
! "UpperDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/diff",
! "WorkDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/work"
},
"Name": "overlay2"
},
"Mounts": [],
"Config": {
! "Hostname": "be9a8ab117d1",
"Domainname": "",
"User": "",
"AttachStdin": false,
详解：
到这里的话，大家是不是大概脑子中是不是有个构思了，就是说容器在创建的时候，里面的目录文件是拼接出来的，为了验证一下这个想法我们继续向下走
了解联合文件系统
root@localhost ~]# docker exec -it web1 bash #再看下web1容器的目录
root@afb553ce70c8:/# ls
a a.txt aa aa.txt aaa aaa.txt bin boot dev docker-entrypoint.d docker-entrypoint.sh etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
root@afb553ce70c8:/# ls docker-entrypoint.d/ #查看这个初始化目录里面都有啥
10-listen-on-ipv6-by-default.sh 20-envsubst-on-templates.sh
###从容器的详细信息里面，按个目录查看一下
[root@localhost ~]# docker inspect web1 | egrep -i data -A 20 -B 1
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa-init/diff:/var/lib/docker/overlay2/9ea913b7611a03e5e6ff79e4ad5966323ddc8d22930fd538b8f4d0cbd8adc6ad/diff:/var/lib/docker/overlay2/4ce0979bb143d9e44e3bab1a8827aec82af2124490824dcd0eded2bdea025543/diff:/var/lib/docker/overlay2/727f637b61409b8760394186a49582dc1bc497a0433074b26fdba053d6263d2b/diff:/var/lib/docker/overlay2/5dbf8694ae45b3211108042719d6ecee8a2aa2c6f59db2e9c7d8a374b5e7e804/diff:/var/lib/docker/overlay2/db778a93aefbc70fd58665217197361951cd31f7edf7a89b1e6f222d9a5e85d6/diff",
"MergedDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/merged",
"UpperDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/diff",
"WorkDir": "/var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/work"
},
"Name": "overlay2"
},
"Mounts": [],
"Config": {
"Hostname": "afb553ce70c8",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"80/tcp": {}
},
"Tty": false,
"OpenStdin": false,
##以下都是 "LowerDir目录里面的
[root@localhost ~]# ls /var/lib/docker/overlay2/9ea913b7611a03e5e6ff79e4ad5966323ddc8d22930fd538b8f4d0cbd8adc6ad/diff
docker-entrypoint.d
[root@localhost ~]# ls /var/lib/docker/overlay2/9ea913b7611a03e5e6ff79e4ad5966323ddc8d22930fd538b8f4d0cbd8adc6ad/diff/docker-entrypoint.d/
20-envsubst-on-templates.sh
[root@localhost ~]# ls /var/lib/docker/overlay2/4ce0979bb143d9e44e3bab1a8827aec82af2124490824dcd0eded2bdea025543/diff
docker-entrypoint.d
[root@localhost ~]# ls /var/lib/docker/overlay2/4ce0979bb143d9e44e3bab1a8827aec82af2124490824dcd0eded2bdea025543/diff/docker-entrypoint.d/
10-listen-on-ipv6-by-default.sh
[root@localhost ~]# ls /var/lib/docker/overlay2/727f637b61409b8760394186a49582dc1bc497a0433074b26fdba053d6263d2b/diff
docker-entrypoint.sh
[root@localhost ~]# ls /var/lib/docker/overlay2/5dbf8694ae45b3211108042719d6ecee8a2aa2c6f59db2e9c7d8a374b5e7e804/diff
docker-entrypoint.d etc lib tmp usr var
[root@localhost ~]# ls /var/lib/docker/overlay2/db778a93aefbc70fd58665217197361951cd31f7edf7a89b1e6f222d9a5e85d6/diff
bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
##这个是"MergedDir"目录里面的内容
[root@localhost ~]# ls /var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/merged
a aa aaa aaa.txt aa.txt a.txt bin boot dev docker-entrypoint.d docker-entrypoint.sh etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
#这个是"UpperDir"目录里面的内容
[root@localhost ~]# ls /var/lib/docker/overlay2/134e38f2b15f44335cfa68fe524f0ebedaaf9e058ab2a1997955a0a4db9483fa/diff
a aa aaa aaa.txt aa.txt a.txt etc root run var通过上面的对比大家可以发现一下几点
- "MergedDir目录就是容器里面的当前目录一模一样
- "LowerDir里面的多个目录下面的文件目录整理在一起的话就是我们在没有创建文件a.txt aa.txt aaa.txt和目录a aa aaa时容器的目录
- "UpperDir"这个目录里面就是我们创建文件a.txt aa.txt aaa.txt和目录a aa aaa的目录，当然了还有人会问这个目录下面还有etc root run var ，为什么，因为你在创建文件和目录的时候这里面有些东西发生了变化
- "UpperDir" + "LowerDir = "MergedDir，小伙子很聪明，看到这里大概也知道了容器的目录是怎么拼起来的吧
让我们来看看web2是不是和我们所说的一样
让我们直接看web2的"UpperDir"吧，，其他的大家自行验证
[root@localhost ~]# docker inspect web2 | grep -i data -A20 -B 1
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459-init/diff:/var/lib/docker/overlay2/9ea913b7611a03e5e6ff79e4ad5966323ddc8d22930fd538b8f4d0cbd8adc6ad/diff:/var/lib/docker/overlay2/4ce0979bb143d9e44e3bab1a8827aec82af2124490824dcd0eded2bdea025543/diff:/var/lib/docker/overlay2/727f637b61409b8760394186a49582dc1bc497a0433074b26fdba053d6263d2b/diff:/var/lib/docker/overlay2/5dbf8694ae45b3211108042719d6ecee8a2aa2c6f59db2e9c7d8a374b5e7e804/diff:/var/lib/docker/overlay2/db778a93aefbc70fd58665217197361951cd31f7edf7a89b1e6f222d9a5e85d6/diff",
"MergedDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/merged",
"UpperDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/diff",
"WorkDir": "/var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/work"
},
"Name": "overlay2"
},
"Mounts": [],
"Config": {
"Hostname": "be9a8ab117d1",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"80/tcp": {}
},
"Tty": false,
"OpenStdin": false,
[root@localhost ~]# ls /var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/diff
b bb bbb bbb.txt bb.txt b.txt etc root run var ##就是我们自己创建的文件和目录，验证完毕解决篇前的疑问
- 为什么创建那么多的容器，磁盘空间不变呢
结束
这就是docker的联合文件系统（UnionFS），你懂了嘛
最后送大家一个福利，为什么我没说那个*****-init目录，大家可以看看[root@localhost ~]# ls /var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459/diff
b bb bbb bbb.txt bb.txt b.txt etc root run var
[root@localhost ~]# ls /var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459-init/diff
dev etc
[root@localhost ~]# ls /var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459-init/diff/dev/
console pts shm
[root@localhost ~]# ls /var/lib/docker/overlay2/2c609b1870a4e9da2c2cdb2f411827250aeebb42a41d165e21caeb1864a10459-init/diff/etc
hostname hosts mtab resolv.conf
## 大家可以看看容器里面的hostname hosts resolv.conf与宿主机的这几个文件有什么区别，开发下同志们的大脑