How to fix Underfull \vbox

Question

I am trying to compile some chapters with the main file thesis.tex in TeXmaker.

After compiling it returns:

 Chapter 4.
 (./chapter/res.tex)
 Underfull \vbox (badness 10000) has occurred while \output is active []
[11
]

I'm new to latex, how can I understand and solve that warning?

that just means you have something that is not big enough to fill the space that it is in. You need to make a small example that shows the problem. — David Carlisle, May 27 '17 at 11:43
Possible duplicate of What are underfull hboxes and vboxes and how can I get rid of them? — TeXnician, May 27 '17 at 11:45
probably it's a big image or table or something on page 10 or 11. — David Carlisle, May 27 '17 at 12:03
I only mentioned it as possible dup, because the other post also relates to getting rid of underfull boxes. — TeXnician, May 27 '17 at 12:23
the example is not useful at all. to make an example start from a copy of your document delete everything after page 10 replace the \input files by copying in the text of the file at that point, then delete all text before the page with the box then delete any packages not needed for the example, that makes an example anyone can run to see the problem. — David Carlisle, May 27 '17 at 13:20
are you sure you want \setlength{\parskip}{1em} that removes all flexibility, and adds a length which is not \baselineskip so any page that just has text and no displayed lists etc but has a paragraph break will necessarily make an underfull box. — David Carlisle, May 27 '17 at 15:33

David Carlisle · Accepted Answer · 2017-05-27T21:09:03.820

You have given very few clues but I assume you have done this

\documentclass[twoside]{report}

\setlength\parskip{1em}

\begin{document}


one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 

one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 
one two three one two three one two three one two three one two three 


\end{document}

which produces the warning

Underfull \vbox (badness 10000) has occurred while \output is active [1

The problem is that the document class has specified that the last line of each page should be at the bottom of the page, but you have removed all flexibility from \parskip and set it to a length which is not a multiple of \baselineskip.

The standard classes default the textheight to be \topskip plus a multiple of \baselineskip precisely to avoid this problem, so a page full of text fits the page exactly. But if you have a page with no stretchable space (so no headings or lists or equations that have stretch space around them) and you have set \parskip to a value that does not stretch, and is not a multiple of \baselineskip then the page inevitably ends short and there is no way to expand it to fill the specified space so it is underfull.

If instead of 1em you set

\setlength\parskip{\baselineskip}

or

\setlength\parskip{1em plus 2pt}

then the warning goes and the bottom line of text is at the bottom of the page.

@santimirandarp texmaker is not involved at all that is just the editor you used to write the file, the warning comes from tex. if you specify that the page height is 40pt high and each line of text is 15pt then if you just have two lines of text you can only have 30pt so the bottom line can not reach the bottom of the text. That never happens normally as the height is a multiple of baselineskip, but if you have 1em every \parskip then every time you have a paragraph break the lines of text are shifted off the spacing and so will not fit at the end of the page. — David Carlisle, May 27 '17 at 21:22
@santimirandarp if the parskip is flexible then each space can expand to cover the shortfall or if \parskip is \baselineskip then the problem does not arise — David Carlisle, May 27 '17 at 21:22
baselineskip is a height from the bottom of the page? and same for topskip? — , May 27 '17 at 21:34
compare with linebreaking. with \raggedright, all word spaces are fixed but the right edge is ragged, with the defaul justified setting the right edge is straight but it can only do that if inter-word space can stretch. with \raggedbottom the bottom of each page varies but with \flushbottom the bottom line is forced to the same position on each page, but that requires stretchy space or ensuring all the fixed lengths add up to the correct total — David Carlisle, May 27 '17 at 21:53
@santimirandarp you gave no usable example so I had to guess. perhaps 2pt was not enough you could use 1em plus 1em for example (but em is not usually used for horizontal specifications) — David Carlisle, May 27 '17 at 21:54

How to fix Underfull \vbox

1 Answers1