Does the Linux kernel need a file system to run?












4















My opinion is yes, it does, because all useful exposure to the outside world (non-priviledged processor mode) would first require a process running in the outside world. That would require a file system, even a temporary, in-RAM, file system.



Another engineer disagrees with me, but I can't seem to prove this beyond all (unknown to me) cases.



Does the answer to this question depend on the definition of 'running'?






filesystems linux-kernel







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Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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  • i think that a running kernel does not "require" useful exposure to the outside world

    – jsotola
    2 hours ago













  • Brings to mind the old halted Linux firewall (circa 2002)

    – Jeff Schaller
    49 mins ago
















4















My opinion is yes, it does, because all useful exposure to the outside world (non-priviledged processor mode) would first require a process running in the outside world. That would require a file system, even a temporary, in-RAM, file system.



Another engineer disagrees with me, but I can't seem to prove this beyond all (unknown to me) cases.



Does the answer to this question depend on the definition of 'running'?






filesystems linux-kernel







share|improve this question







New contributor




Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





















  • i think that a running kernel does not "require" useful exposure to the outside world

    – jsotola
    2 hours ago













  • Brings to mind the old halted Linux firewall (circa 2002)

    – Jeff Schaller
    49 mins ago














4












4








4








My opinion is yes, it does, because all useful exposure to the outside world (non-priviledged processor mode) would first require a process running in the outside world. That would require a file system, even a temporary, in-RAM, file system.



Another engineer disagrees with me, but I can't seem to prove this beyond all (unknown to me) cases.



Does the answer to this question depend on the definition of 'running'?






filesystems linux-kernel







share|improve this question







New contributor




Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












My opinion is yes, it does, because all useful exposure to the outside world (non-priviledged processor mode) would first require a process running in the outside world. That would require a file system, even a temporary, in-RAM, file system.



Another engineer disagrees with me, but I can't seem to prove this beyond all (unknown to me) cases.



Does the answer to this question depend on the definition of 'running'?






filesystems linux-kernel




filesystems linux-kernel






share|improve this question







New contributor




Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|improve this question







New contributor




Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this question




share|improve this question






New contributor




Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked 2 hours ago









Peter L.Peter L.

1213




1213




New contributor




Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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New contributor





Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Peter L. is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.













  • i think that a running kernel does not "require" useful exposure to the outside world

    – jsotola
    2 hours ago













  • Brings to mind the old halted Linux firewall (circa 2002)

    – Jeff Schaller
    49 mins ago



















  • i think that a running kernel does not "require" useful exposure to the outside world

    – jsotola
    2 hours ago













  • Brings to mind the old halted Linux firewall (circa 2002)

    – Jeff Schaller
    49 mins ago

















i think that a running kernel does not "require" useful exposure to the outside world

– jsotola
2 hours ago







i think that a running kernel does not "require" useful exposure to the outside world

– jsotola
2 hours ago















Brings to mind the old halted Linux firewall (circa 2002)

– Jeff Schaller
49 mins ago





Brings to mind the old halted Linux firewall (circa 2002)

– Jeff Schaller
49 mins ago










2 Answers
2






active

oldest

votes


















3














That's rather an odd question because you don't run the kernel like you run a program. The kernel is a platform to run programs on. Of course there is setup and shutdown code but it's not possible to run the kernel on its own. There must always be a main "init" process. And the kernel will panic if it's not there. If init tries to exit the kernel will also panic.



These days the init process is something like systemd. If not otherwise specified the kernel will try to run a program starting with /sbin/init. See the init Param here http://man7.org/linux/man-pages/man7/bootparam.7.html in an emergency you can boot Linux with init=/bin/bash . But notice how you always specify a file on the file system to run.



So the kernel will panic if it starts up an has no file system because without one there is no way to load init.



Some confusion may arise because of a chicken and egg situation where the kernel must load drivers to access it's file system. To get round this an initial ramdisk is loaded from an image on disk containing vital drivers and setup scripts. These are executed before the file system is loaded. But make no mistake the initial ramdisk is itself a file system.






share|improve this answer


























  • Isn't there a condition where the kernel gives up trying to initialize hardware and load a known file system (not initrd passed into the kernel via init params), then drops into a very limited shell (without init=/bin/bash)? Also, since you bring up /bin/bash, would the kernel always have that minimal file system available, even if it was built with other .config options that could potentially eliminate this?

    – Peter L.
    59 mins ago



















2














In Linux, every device is a file, so you have to have a filesystem to run it.






share|improve this answer



















  • 1





    But of course the device drivers exist inside the kernel irrespective of whether or not a device file points to them.

    – Philip Couling
    1 hour ago











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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









3














That's rather an odd question because you don't run the kernel like you run a program. The kernel is a platform to run programs on. Of course there is setup and shutdown code but it's not possible to run the kernel on its own. There must always be a main "init" process. And the kernel will panic if it's not there. If init tries to exit the kernel will also panic.



These days the init process is something like systemd. If not otherwise specified the kernel will try to run a program starting with /sbin/init. See the init Param here http://man7.org/linux/man-pages/man7/bootparam.7.html in an emergency you can boot Linux with init=/bin/bash . But notice how you always specify a file on the file system to run.



So the kernel will panic if it starts up an has no file system because without one there is no way to load init.



Some confusion may arise because of a chicken and egg situation where the kernel must load drivers to access it's file system. To get round this an initial ramdisk is loaded from an image on disk containing vital drivers and setup scripts. These are executed before the file system is loaded. But make no mistake the initial ramdisk is itself a file system.






share|improve this answer


























  • Isn't there a condition where the kernel gives up trying to initialize hardware and load a known file system (not initrd passed into the kernel via init params), then drops into a very limited shell (without init=/bin/bash)? Also, since you bring up /bin/bash, would the kernel always have that minimal file system available, even if it was built with other .config options that could potentially eliminate this?

    – Peter L.
    59 mins ago
















3














That's rather an odd question because you don't run the kernel like you run a program. The kernel is a platform to run programs on. Of course there is setup and shutdown code but it's not possible to run the kernel on its own. There must always be a main "init" process. And the kernel will panic if it's not there. If init tries to exit the kernel will also panic.



These days the init process is something like systemd. If not otherwise specified the kernel will try to run a program starting with /sbin/init. See the init Param here http://man7.org/linux/man-pages/man7/bootparam.7.html in an emergency you can boot Linux with init=/bin/bash . But notice how you always specify a file on the file system to run.



So the kernel will panic if it starts up an has no file system because without one there is no way to load init.



Some confusion may arise because of a chicken and egg situation where the kernel must load drivers to access it's file system. To get round this an initial ramdisk is loaded from an image on disk containing vital drivers and setup scripts. These are executed before the file system is loaded. But make no mistake the initial ramdisk is itself a file system.






share|improve this answer


























  • Isn't there a condition where the kernel gives up trying to initialize hardware and load a known file system (not initrd passed into the kernel via init params), then drops into a very limited shell (without init=/bin/bash)? Also, since you bring up /bin/bash, would the kernel always have that minimal file system available, even if it was built with other .config options that could potentially eliminate this?

    – Peter L.
    59 mins ago














3












3








3







That's rather an odd question because you don't run the kernel like you run a program. The kernel is a platform to run programs on. Of course there is setup and shutdown code but it's not possible to run the kernel on its own. There must always be a main "init" process. And the kernel will panic if it's not there. If init tries to exit the kernel will also panic.



These days the init process is something like systemd. If not otherwise specified the kernel will try to run a program starting with /sbin/init. See the init Param here http://man7.org/linux/man-pages/man7/bootparam.7.html in an emergency you can boot Linux with init=/bin/bash . But notice how you always specify a file on the file system to run.



So the kernel will panic if it starts up an has no file system because without one there is no way to load init.



Some confusion may arise because of a chicken and egg situation where the kernel must load drivers to access it's file system. To get round this an initial ramdisk is loaded from an image on disk containing vital drivers and setup scripts. These are executed before the file system is loaded. But make no mistake the initial ramdisk is itself a file system.






share|improve this answer















That's rather an odd question because you don't run the kernel like you run a program. The kernel is a platform to run programs on. Of course there is setup and shutdown code but it's not possible to run the kernel on its own. There must always be a main "init" process. And the kernel will panic if it's not there. If init tries to exit the kernel will also panic.



These days the init process is something like systemd. If not otherwise specified the kernel will try to run a program starting with /sbin/init. See the init Param here http://man7.org/linux/man-pages/man7/bootparam.7.html in an emergency you can boot Linux with init=/bin/bash . But notice how you always specify a file on the file system to run.



So the kernel will panic if it starts up an has no file system because without one there is no way to load init.



Some confusion may arise because of a chicken and egg situation where the kernel must load drivers to access it's file system. To get round this an initial ramdisk is loaded from an image on disk containing vital drivers and setup scripts. These are executed before the file system is loaded. But make no mistake the initial ramdisk is itself a file system.







share|improve this answer














share|improve this answer



share|improve this answer








edited 1 hour ago

























answered 1 hour ago









Philip CoulingPhilip Couling

2,011920




2,011920













  • Isn't there a condition where the kernel gives up trying to initialize hardware and load a known file system (not initrd passed into the kernel via init params), then drops into a very limited shell (without init=/bin/bash)? Also, since you bring up /bin/bash, would the kernel always have that minimal file system available, even if it was built with other .config options that could potentially eliminate this?

    – Peter L.
    59 mins ago



















  • Isn't there a condition where the kernel gives up trying to initialize hardware and load a known file system (not initrd passed into the kernel via init params), then drops into a very limited shell (without init=/bin/bash)? Also, since you bring up /bin/bash, would the kernel always have that minimal file system available, even if it was built with other .config options that could potentially eliminate this?

    – Peter L.
    59 mins ago

















Isn't there a condition where the kernel gives up trying to initialize hardware and load a known file system (not initrd passed into the kernel via init params), then drops into a very limited shell (without init=/bin/bash)? Also, since you bring up /bin/bash, would the kernel always have that minimal file system available, even if it was built with other .config options that could potentially eliminate this?

– Peter L.
59 mins ago





Isn't there a condition where the kernel gives up trying to initialize hardware and load a known file system (not initrd passed into the kernel via init params), then drops into a very limited shell (without init=/bin/bash)? Also, since you bring up /bin/bash, would the kernel always have that minimal file system available, even if it was built with other .config options that could potentially eliminate this?

– Peter L.
59 mins ago













2














In Linux, every device is a file, so you have to have a filesystem to run it.






share|improve this answer



















  • 1





    But of course the device drivers exist inside the kernel irrespective of whether or not a device file points to them.

    – Philip Couling
    1 hour ago
















2














In Linux, every device is a file, so you have to have a filesystem to run it.






share|improve this answer



















  • 1





    But of course the device drivers exist inside the kernel irrespective of whether or not a device file points to them.

    – Philip Couling
    1 hour ago














2












2








2







In Linux, every device is a file, so you have to have a filesystem to run it.






share|improve this answer













In Linux, every device is a file, so you have to have a filesystem to run it.







share|improve this answer












share|improve this answer



share|improve this answer










answered 2 hours ago









K7AAYK7AAY

744825




744825








  • 1





    But of course the device drivers exist inside the kernel irrespective of whether or not a device file points to them.

    – Philip Couling
    1 hour ago














  • 1





    But of course the device drivers exist inside the kernel irrespective of whether or not a device file points to them.

    – Philip Couling
    1 hour ago








1




1





But of course the device drivers exist inside the kernel irrespective of whether or not a device file points to them.

– Philip Couling
1 hour ago





But of course the device drivers exist inside the kernel irrespective of whether or not a device file points to them.

– Philip Couling
1 hour ago










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