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I am wondering if there is any historical or practical reason why the umount command is not unmount.

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up vote 57 down vote accepted

This dates all the way back to the very first edition of Unix, where all the standard file names were only at most 6 characters long (think passwd), even though this version supported a whooping 8 characters in a file name. Most commands had an associated source file ending in .c (e.g. umount.c), which left only 6 characters for the base name.

A 6-character limitation might also have been a holdover from an earlier development version, or inherited from a then-current IBM system that did have a 6-character limitation. (Early C implementations had a 6-character limit on identifiers — longer identifiers were accepted but the compiler only looked at the first 6 characters, so foobar1 and foobar2 were the same variable.)

(I thought I remembered a umount man page that listed the spelling as a bug of unknown origin, but I can't find it now.)

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6 character command name + .c (or .s) extension = 8 character filename limit. – geekosaur Mar 21 '11 at 21:25
@geekosaur: Ah, right, the source file. If you write an answer, I'll delete mine. – Gilles Mar 21 '11 at 21:37
Enh, just annotate it if you want. – geekosaur Mar 21 '11 at 21:38
@geekosaur: I thought of the man page, as well, but V1 didn't have a man command (and one of the man pages is called directory, which wouldn't have fit yet). So I wonder why passwd was truncated to 6 characters (there wasn't a passwd command yet either, just /etc/passwd). – Gilles Mar 21 '11 at 22:52
Thank you! @geekosaur: +1 for your comment :) – uloBasEI Mar 23 '11 at 21:52

For the same reason the creat system call is not spelled create ?


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Nope. The regret in the quote you reference is because they could have added the 'e' even in spite of the 6 character limit being argued over in the other answer. There really is no good reason for it to be truncated, unlike with umount. – Warren Young Mar 22 '11 at 2:50
I'm guessing by that time it was tradition to truncate letters if you could. – Shadur Mar 22 '11 at 8:00

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