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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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2 Answers 2

up vote 43 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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14  
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
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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 ?

http://stackoverflow.com/questions/1713457/what-did-ken-thompson-mean-when-he-said-id-spell-create-with-an-e

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2  
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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