最後更新: 2021-08-25

目錄

• Container 的 mount 設定
• Bind mount
• Mount Example / Test
• fuse
• doc

 

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Container 的 mount 設定

 

方法

• 方式1: 透過另一個設定檔去設定 mount 什麼(lxc.mount=/path/to/fstab)
• 方式2: 在同一個 config file 內設定(lxc.mount.entry=...)

方式1: 透過另一個設定檔去設定 mount 什麼

lxc.mount = /var/lib/lxc/mx5/fstab

/var/lib/lxc/mx5/fstab:

proc            proc         proc  nodev,noexec,nosuid 0 0
sysfs           sys          sysfs defaults            0 0

方式2: 在同一個 config file 內設定

lxc.mount.entry = proc  /var/lib/lxc/centos6/rootfs/proc proc  nodev,noexec,nosuid 0 0
lxc.mount.entry = sysfs /var/lib/lxc/centos6/rootfs/sys  sysfs defaults,ro         0 0

relative destination path

* relative path is taken to be relative to the mounted container root

i.e. Host 的 /home/data mount 到 Container 的 /home/data

lxc.mount.entry = /home/data    home/data     none bind 0 0

i.e. Container 的 /dev/null mount 到 Container 的 /proc/kcore

dev/null proc/kcore none bind,relative 0 0

File / Folder Owner

If the host's user does not exist in the container, the container will still be mounted,

 but with nobody:nogroup as the owner

Additional mount options

• "optional"        # don't fail if mount does not work
• "create=dir"    # to create dir (or file) when the point will be mounted.
• "create=file"

 

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Bind mount

 

* container 有自己的 mounts namespace => can’t just mount it

 => 在 vps start 前已 mount 入去才有效

# 建立 folder

mkdir /backup/shared

# turn the directory into a "bind mount"

mount --bind /backup/shared /backup/shared

Remark: shortoption

mount -B olddir newdir

行 cmd mount 時會見到

/backup/shared on /backup/shared type none (rw,bind)

# 令它不被任何 container mount

mount --make-unbindable /shared

# 令其可以被 mount

mount --make-slave /backup/shared

Remark

The shared subtrees operations:

* private - does not forward or receive propagation (Default)

* slave - receives propagation from its master

* shared - provides ability to create mirrors of that mount

  (any mount within the original mount point is reflected in it, and vice versa.)

* unbindable - mount is a private mount which cannot be cloned through a bind operation

Checking

/backup/shared on /backup/shared type none (rw,bind,make-slave)

fstab

/backup/shared  /backup/shared  none  bind  0 0

vps config

mkdir /lxc/sshgw/rootfs/mnt/shared/

方式 1

/var/lib/lxc/sshgw/fstab

/dev/sda1 on /mnt/shared type ext4 (rw,noatime,user_xattr,barrier=1,data=ordered)

方式 2

/lxc/sshgw/config

# In the lxc.mount.entry, it’s generally recommented now to use the relative pathname for the target.

lxc.mount.entry = /backup/shared mnt/shared none defaults,noatime,bind 0 0

--rbind (-R)

* The --bind mount call attaches only a single filesystem, not possible submounts.

   --rbind  => The entire file hierarchy including submounts is attached

mount --rbind olddir newdir

 

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Mount Example / Test

 

目錄

• slave mount example
• make the mount at /cdrom shared
• unbindable usage

slave mount

mkdir MasterFolder SlaveFolder

mkdir MasterFolder/a MasterFolder/b

mount --bind /root/MasterFolder /root/SlaveFolder

mount --make-slave /root/SlaveFolder

mount /dev/sde1 /root/SlaveFolder/b

ls /root/MasterFolder/b

ls /root/SlaveFolder/b

s1 s2 s3

make the mount at /cdrom shared

mount --bind /cdrom /cdrom

mount --make-shared /cdrom

So when a CD is inserted and mounted at /cdrom that mount gets

propagated to the other mount at /cdrom in all the other clone namespaces.

unbindable usage

mount --bind /root/test1 /root/test1

mount --make-unbindable /root/test1

mount --bind /root/test1/ /root/test2

mount: wrong fs type, bad option, bad superblock on /root/test1,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

Q1. Why is bind mount needed? How is it different from symbolic links?

symbolic links can get stale if the destination mount gets unmounted or moved.

Bind mounts continue to exist even if the other mount is unmounted or moved.

Q2. Why is unbindable mount needed?

                    root
                   /    \
                  tmp    usr

mount --bind /root/tmp /root/tmp

mount --make-rshared /root

mount --make-unbindable /root/tmp

mkdir -p /tmp/m1

mount --rbind /root /tmp/m1

mkdir -p /tmp/m2

mount --rbind /root /tmp/m2

mkdir -p /tmp/m3

mount --rbind /root /tmp/m3

        root
     /         \
    tmp       usr
    /    \       \
  m1     m2      m3
 /  \     / \    /  \
tmp  usr tmp usr tmp usr

 

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fuse

 

 

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Doc

 

https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt

 

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