man/man2/umount.2

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.he 'UMOUNT (II)'3/15/72'UMOUNT (II)'
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NAME            umount  -- dismount file system
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SYNOPSIS        sys umount; special  / umount = 22.
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DESCRIPTION     umount\b\b\b\b\b\b______
announces to the system that special
file special\b\b\b\b\b\b\b_______ is no longer to contain
a removable file system.
The file associated with the special
file reverts to its ordinary interpretation (see mount\b\b\b\b\b_____).

The user must take
care that all activity on the file system has ceased.
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SEE ALSO        umount(I), mount(II)
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DIAGNOSTICS     Error bit
(c-bit) set if
no
file system was mounted on the special file.
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BUGS            Use
of this call should
be restricted to the super-user.