Does order of mount operations matter when mounting into an existing mountpoint?












5














The question Best practice when mounting a new disk within an existing mount?
inspired me to ask this follow-up question:



The other question asked whether it is ok to 



mount /dev/sdb1 /home

mount /dev/sdb2 /home/mythtv


so that /home/mythtv is a mountpoint within the mountpoint
/home. (spoiler: Yes, it is perfectly ok.).



What if I'd change the order of commands to



mount /dev/sdb2 /home/mythtv

mount /dev/sdb1 /home


Will that yield the same result or will /home/mythtv be hidden by /home?
I assume /home contains an (empty) directory /home/mythtv.






mount







share|improve this question



























    5














    The question Best practice when mounting a new disk within an existing mount?
    inspired me to ask this follow-up question:



    The other question asked whether it is ok to 



    mount /dev/sdb1 /home
    
mount /dev/sdb2 /home/mythtv


    so that /home/mythtv is a mountpoint within the mountpoint
    /home. (spoiler: Yes, it is perfectly ok.).



    What if I'd change the order of commands to



    mount /dev/sdb2 /home/mythtv
    
mount /dev/sdb1 /home


    Will that yield the same result or will /home/mythtv be hidden by /home?
    I assume /home contains an (empty) directory /home/mythtv.






    mount







    share|improve this question

























      5












      5








      5







      The question Best practice when mounting a new disk within an existing mount?
      inspired me to ask this follow-up question:



      The other question asked whether it is ok to 



      mount /dev/sdb1 /home
      
mount /dev/sdb2 /home/mythtv


      so that /home/mythtv is a mountpoint within the mountpoint
      /home. (spoiler: Yes, it is perfectly ok.).



      What if I'd change the order of commands to



      mount /dev/sdb2 /home/mythtv
      
mount /dev/sdb1 /home


      Will that yield the same result or will /home/mythtv be hidden by /home?
      I assume /home contains an (empty) directory /home/mythtv.






      mount







      share|improve this question













      The question Best practice when mounting a new disk within an existing mount?
      inspired me to ask this follow-up question:



      The other question asked whether it is ok to 



      mount /dev/sdb1 /home
      
mount /dev/sdb2 /home/mythtv


      so that /home/mythtv is a mountpoint within the mountpoint
      /home. (spoiler: Yes, it is perfectly ok.).



      What if I'd change the order of commands to



      mount /dev/sdb2 /home/mythtv
      
mount /dev/sdb1 /home


      Will that yield the same result or will /home/mythtv be hidden by /home?
      I assume /home contains an (empty) directory /home/mythtv.






      mount




      mount






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked 17 hours ago









      PerlDuck

      5,43911231




      5,43911231






















          1 Answer
          1






          active

          oldest

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          11














          Yes, it matters! Your first example:



          mount /dev/sdb1 /home
          
mount /dev/sdb2 /home/mythtv


          is the only right way, when mounting you must respect the tree order.



          In your second example,



          mount /dev/sdb2 /home/mythtv
          
mount /dev/sdb1 /home


          If we are assuming /home/mythtv exists on the filesystem, it is gonna mount it with no problem, but after you mount the second volume you won't be able to access the first one anymore.



          This is because you let the system mount sdb2 on an existing path at /home/mythtv. When you mount on /home/, you are telling your system to mount it on the /home path which also exists but is going to "cover" existing mount point. They are both mounted, but when you type cd /home/mythtv, Bash takes you to sdb1:/home/mythtv instead sdb2:/home/mythtv because they are different paths.



          I hope the explanation is clear. If not, please ask in the comments, I'll try to get it to you more clearly.



          Update



          as per @mook765's comment, the order is important also in the fstab files:



          The fstab file is read up to down while mounting, and down to up when umounting. In another case, if you try to umount /home before /home/mythtv mount will tell you the /home resource is busy because you have the /home/mythtv mounted and it cannot handle it.






          share|improve this answer























          • Yes, that sounds reasonable. Thank you.
            – PerlDuck
            16 hours ago






          • 2




            @PerlDuck This is also important for /etc/fstab, line order matters.
            – mook765
            16 hours ago






          • 1




            Yes Absolutely, @mook765 say the true, fstab file when mount is read up to down, and when umount down to up, in other case if you try to umount /home before /home/mythtv mount will say to you the /home resource is busy, because have the /home/mythtv mounted and cannot handle it.
            – AtomiX84
            16 hours ago












          • In which cases would /etc/fstab be used for unmounting? The only thing I could think of is umount -a, but that command looks at what's actually mounted, not /etc/fstab.
            – kasperd
            12 hours ago










          • by reading here seems it also used by umount: man7.org/linux/man-pages/man5/fstab.5.html, anyway after thinking a while on this (if you can confirm to me) the umount go to read the fstab when you invoke: umount /mount/point. But I repeat, may I misunderstanding the process of umount, the mount I'm sure is gonna to work like I had describe.
            – AtomiX84
            9 hours ago











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          1 Answer
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          1 Answer
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          11














          Yes, it matters! Your first example:



          mount /dev/sdb1 /home
          
mount /dev/sdb2 /home/mythtv


          is the only right way, when mounting you must respect the tree order.



          In your second example,



          mount /dev/sdb2 /home/mythtv
          
mount /dev/sdb1 /home


          If we are assuming /home/mythtv exists on the filesystem, it is gonna mount it with no problem, but after you mount the second volume you won't be able to access the first one anymore.



          This is because you let the system mount sdb2 on an existing path at /home/mythtv. When you mount on /home/, you are telling your system to mount it on the /home path which also exists but is going to "cover" existing mount point. They are both mounted, but when you type cd /home/mythtv, Bash takes you to sdb1:/home/mythtv instead sdb2:/home/mythtv because they are different paths.



          I hope the explanation is clear. If not, please ask in the comments, I'll try to get it to you more clearly.



          Update



          as per @mook765's comment, the order is important also in the fstab files:



          The fstab file is read up to down while mounting, and down to up when umounting. In another case, if you try to umount /home before /home/mythtv mount will tell you the /home resource is busy because you have the /home/mythtv mounted and it cannot handle it.






          share|improve this answer























          • Yes, that sounds reasonable. Thank you.
            – PerlDuck
            16 hours ago






          • 2




            @PerlDuck This is also important for /etc/fstab, line order matters.
            – mook765
            16 hours ago






          • 1




            Yes Absolutely, @mook765 say the true, fstab file when mount is read up to down, and when umount down to up, in other case if you try to umount /home before /home/mythtv mount will say to you the /home resource is busy, because have the /home/mythtv mounted and cannot handle it.
            – AtomiX84
            16 hours ago












          • In which cases would /etc/fstab be used for unmounting? The only thing I could think of is umount -a, but that command looks at what's actually mounted, not /etc/fstab.
            – kasperd
            12 hours ago










          • by reading here seems it also used by umount: man7.org/linux/man-pages/man5/fstab.5.html, anyway after thinking a while on this (if you can confirm to me) the umount go to read the fstab when you invoke: umount /mount/point. But I repeat, may I misunderstanding the process of umount, the mount I'm sure is gonna to work like I had describe.
            – AtomiX84
            9 hours ago
















          11














          Yes, it matters! Your first example:



          mount /dev/sdb1 /home
          
mount /dev/sdb2 /home/mythtv


          is the only right way, when mounting you must respect the tree order.



          In your second example,



          mount /dev/sdb2 /home/mythtv
          
mount /dev/sdb1 /home


          If we are assuming /home/mythtv exists on the filesystem, it is gonna mount it with no problem, but after you mount the second volume you won't be able to access the first one anymore.



          This is because you let the system mount sdb2 on an existing path at /home/mythtv. When you mount on /home/, you are telling your system to mount it on the /home path which also exists but is going to "cover" existing mount point. They are both mounted, but when you type cd /home/mythtv, Bash takes you to sdb1:/home/mythtv instead sdb2:/home/mythtv because they are different paths.



          I hope the explanation is clear. If not, please ask in the comments, I'll try to get it to you more clearly.



          Update



          as per @mook765's comment, the order is important also in the fstab files:



          The fstab file is read up to down while mounting, and down to up when umounting. In another case, if you try to umount /home before /home/mythtv mount will tell you the /home resource is busy because you have the /home/mythtv mounted and it cannot handle it.






          share|improve this answer























          • Yes, that sounds reasonable. Thank you.
            – PerlDuck
            16 hours ago






          • 2




            @PerlDuck This is also important for /etc/fstab, line order matters.
            – mook765
            16 hours ago






          • 1




            Yes Absolutely, @mook765 say the true, fstab file when mount is read up to down, and when umount down to up, in other case if you try to umount /home before /home/mythtv mount will say to you the /home resource is busy, because have the /home/mythtv mounted and cannot handle it.
            – AtomiX84
            16 hours ago












          • In which cases would /etc/fstab be used for unmounting? The only thing I could think of is umount -a, but that command looks at what's actually mounted, not /etc/fstab.
            – kasperd
            12 hours ago










          • by reading here seems it also used by umount: man7.org/linux/man-pages/man5/fstab.5.html, anyway after thinking a while on this (if you can confirm to me) the umount go to read the fstab when you invoke: umount /mount/point. But I repeat, may I misunderstanding the process of umount, the mount I'm sure is gonna to work like I had describe.
            – AtomiX84
            9 hours ago














          11












          11








          11






          Yes, it matters! Your first example:



          mount /dev/sdb1 /home
          
mount /dev/sdb2 /home/mythtv


          is the only right way, when mounting you must respect the tree order.



          In your second example,



          mount /dev/sdb2 /home/mythtv
          
mount /dev/sdb1 /home


          If we are assuming /home/mythtv exists on the filesystem, it is gonna mount it with no problem, but after you mount the second volume you won't be able to access the first one anymore.



          This is because you let the system mount sdb2 on an existing path at /home/mythtv. When you mount on /home/, you are telling your system to mount it on the /home path which also exists but is going to "cover" existing mount point. They are both mounted, but when you type cd /home/mythtv, Bash takes you to sdb1:/home/mythtv instead sdb2:/home/mythtv because they are different paths.



          I hope the explanation is clear. If not, please ask in the comments, I'll try to get it to you more clearly.



          Update



          as per @mook765's comment, the order is important also in the fstab files:



          The fstab file is read up to down while mounting, and down to up when umounting. In another case, if you try to umount /home before /home/mythtv mount will tell you the /home resource is busy because you have the /home/mythtv mounted and it cannot handle it.






          share|improve this answer














          Yes, it matters! Your first example:



          mount /dev/sdb1 /home
          
mount /dev/sdb2 /home/mythtv


          is the only right way, when mounting you must respect the tree order.



          In your second example,



          mount /dev/sdb2 /home/mythtv
          
mount /dev/sdb1 /home


          If we are assuming /home/mythtv exists on the filesystem, it is gonna mount it with no problem, but after you mount the second volume you won't be able to access the first one anymore.



          This is because you let the system mount sdb2 on an existing path at /home/mythtv. When you mount on /home/, you are telling your system to mount it on the /home path which also exists but is going to "cover" existing mount point. They are both mounted, but when you type cd /home/mythtv, Bash takes you to sdb1:/home/mythtv instead sdb2:/home/mythtv because they are different paths.



          I hope the explanation is clear. If not, please ask in the comments, I'll try to get it to you more clearly.



          Update



          as per @mook765's comment, the order is important also in the fstab files:



          The fstab file is read up to down while mounting, and down to up when umounting. In another case, if you try to umount /home before /home/mythtv mount will tell you the /home resource is busy because you have the /home/mythtv mounted and it cannot handle it.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 14 hours ago









          Dan

          6,97434373




          6,97434373










          answered 17 hours ago









          AtomiX84

          32018




          32018












          • Yes, that sounds reasonable. Thank you.
            – PerlDuck
            16 hours ago






          • 2




            @PerlDuck This is also important for /etc/fstab, line order matters.
            – mook765
            16 hours ago






          • 1




            Yes Absolutely, @mook765 say the true, fstab file when mount is read up to down, and when umount down to up, in other case if you try to umount /home before /home/mythtv mount will say to you the /home resource is busy, because have the /home/mythtv mounted and cannot handle it.
            – AtomiX84
            16 hours ago












          • In which cases would /etc/fstab be used for unmounting? The only thing I could think of is umount -a, but that command looks at what's actually mounted, not /etc/fstab.
            – kasperd
            12 hours ago










          • by reading here seems it also used by umount: man7.org/linux/man-pages/man5/fstab.5.html, anyway after thinking a while on this (if you can confirm to me) the umount go to read the fstab when you invoke: umount /mount/point. But I repeat, may I misunderstanding the process of umount, the mount I'm sure is gonna to work like I had describe.
            – AtomiX84
            9 hours ago


















          • Yes, that sounds reasonable. Thank you.
            – PerlDuck
            16 hours ago






          • 2




            @PerlDuck This is also important for /etc/fstab, line order matters.
            – mook765
            16 hours ago






          • 1




            Yes Absolutely, @mook765 say the true, fstab file when mount is read up to down, and when umount down to up, in other case if you try to umount /home before /home/mythtv mount will say to you the /home resource is busy, because have the /home/mythtv mounted and cannot handle it.
            – AtomiX84
            16 hours ago












          • In which cases would /etc/fstab be used for unmounting? The only thing I could think of is umount -a, but that command looks at what's actually mounted, not /etc/fstab.
            – kasperd
            12 hours ago










          • by reading here seems it also used by umount: man7.org/linux/man-pages/man5/fstab.5.html, anyway after thinking a while on this (if you can confirm to me) the umount go to read the fstab when you invoke: umount /mount/point. But I repeat, may I misunderstanding the process of umount, the mount I'm sure is gonna to work like I had describe.
            – AtomiX84
            9 hours ago
















          Yes, that sounds reasonable. Thank you.
          – PerlDuck
          16 hours ago




          Yes, that sounds reasonable. Thank you.
          – PerlDuck
          16 hours ago




          2




          2




          @PerlDuck This is also important for /etc/fstab, line order matters.
          – mook765
          16 hours ago




          @PerlDuck This is also important for /etc/fstab, line order matters.
          – mook765
          16 hours ago




          1




          1




          Yes Absolutely, @mook765 say the true, fstab file when mount is read up to down, and when umount down to up, in other case if you try to umount /home before /home/mythtv mount will say to you the /home resource is busy, because have the /home/mythtv mounted and cannot handle it.
          – AtomiX84
          16 hours ago






          Yes Absolutely, @mook765 say the true, fstab file when mount is read up to down, and when umount down to up, in other case if you try to umount /home before /home/mythtv mount will say to you the /home resource is busy, because have the /home/mythtv mounted and cannot handle it.
          – AtomiX84
          16 hours ago














          In which cases would /etc/fstab be used for unmounting? The only thing I could think of is umount -a, but that command looks at what's actually mounted, not /etc/fstab.
          – kasperd
          12 hours ago




          In which cases would /etc/fstab be used for unmounting? The only thing I could think of is umount -a, but that command looks at what's actually mounted, not /etc/fstab.
          – kasperd
          12 hours ago












          by reading here seems it also used by umount: man7.org/linux/man-pages/man5/fstab.5.html, anyway after thinking a while on this (if you can confirm to me) the umount go to read the fstab when you invoke: umount /mount/point. But I repeat, may I misunderstanding the process of umount, the mount I'm sure is gonna to work like I had describe.
          – AtomiX84
          9 hours ago




          by reading here seems it also used by umount: man7.org/linux/man-pages/man5/fstab.5.html, anyway after thinking a while on this (if you can confirm to me) the umount go to read the fstab when you invoke: umount /mount/point. But I repeat, may I misunderstanding the process of umount, the mount I'm sure is gonna to work like I had describe.
          – AtomiX84
          9 hours ago


















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