[lilypond.git] / Documentation / usage / running.itely

@c -*- coding: utf-8; mode: texinfo; -*-

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@c \version "2.17.6"


@node Running lilypond
@chapter Running @command{lilypond}

This chapter details the technicalities of running LilyPond.

@menu
* Normal usage::
* Command-line usage::
* Error messages::
* Common errors::
@end menu


@node Normal usage
@section Normal usage

Most users run LilyPond through a GUI; if you have not done so
already, please read the @rlearning{Tutorial}.  If you use an alternate
editor to write lilypond files, see the documentation for that
program.


@node Command-line usage
@section Command-line usage

This section contains extra information about using LilyPond on the
command-line.  This may be desirable to pass extra options to the
program.  In addition, there are certain extra @q{helper} programs (such
as @code{midi2ly}) which are only available on the command-line.

By @q{command-line}, we mean the command line in the operating system.
Windows users might be more familiar with the terms @q{DOS shell} or
@q{command shell}.  MacOS@tie{}X users might be more familiar with the terms
@q{terminal} or @q{console}.  Some additional setup is required
for MacOS@tie{}X users; please see @rweb{MacOS X}.

Describing how to use this part of an operating system is outside the
scope of this manual; please consult other documentation on this topic
if you are unfamiliar with the command-line.

@menu
* Invoking LilyPond::
* Basic command line options for LilyPond::
* Advanced command line options for LilyPond::
* Environment variables::
* LilyPond in chroot jail::
@end menu

@node Invoking LilyPond
@unnumberedsubsec Invoking @command{lilypond}

The @command{lilypond} executable may be called as follows from
the command line.

@example
lilypond [@var{option}]@dots{} @var{file}@dots{}
@end example

When invoked with a filename that has no extension, the @file{.ly}
extension is tried first.  To read input from stdin, use a
dash (@code{-}) for @var{file}.

When @file{filename.ly} is processed it will produce @file{filename.ps}
and @file{filename.pdf} as output.  Several files can be specified;
they will each be processed independently.  @footnote{The status of
GUILE is not reset after processing a @code{.ly} file, so be careful
not to change any system defaults from within Scheme.}

If @file{filename.ly} contains more than one @code{\book}
block, then the rest of the scores will be output in numbered files,
starting with @file{filename-1.pdf}.  In addition, the value of
@code{output-suffix} will be inserted between the basename and the
number.  An input file containing

@example
#(define output-suffix "violin")
\score @{ @dots{} @}
#(define output-suffix "cello")
\score @{ @dots{} @}
@end example

@noindent
will output @var{base}@file{-violin.pdf} and
@var{base}@file{-cello-1.pdf}.


@unnumberedsubsubsec Using LilyPond with standard shell features

Since LilyPond is a command line application, features of the @q{shell}
used for calling LilyPond can also be put to good use.

For example:

@example
lilypond *.ly
@end example

@noindent
will process all LilyPond files in the current directory.

Redirecting the console output (e.g. to a file) may also be useful:

@example
lilypond file.ly 1> stdout.txt

lilypond file.ly 2> stderr.txt

lilypond file.ly &> all.txt
@end example

@noindent
Redirects @q{normal} output, @q{errors} only or @q{everything},
respectively, to a text file.  Consult the documentation for your
particular shell, Command (Windows), Terminal or Console
applications (MacOS X) to see if output redirection is supported or if
the syntax is different.


@node Basic command line options for LilyPond
@unnumberedsubsec Basic command line options for LilyPond

@cindex Invoking @command{lilypond}
@cindex command line options for @command{lilypond}
@cindex options, command line
@cindex switches

The following options are supported:

@table @code

@item -d, --define-default=@var{var}=@var{val}
See @ref{Advanced command line options for LilyPond}.

@cindex Scheme, expression evaluation
@cindex expression evaluation, Scheme

@item -e, --evaluate=@var{expr}
Evaluate the Scheme @var{expr} before parsing any @file{.ly} files.
Multiple @option{-e} options may be given, they will be evaluated
sequentially.

The expression will be evaluated in the @code{guile-user} module, so
if you want to use definitions in @var{expr}, use

@example
lilypond -e '(define-public a 42)'
@end example

@noindent
on the command-line, and include

@example
#(use-modules (guile-user))
@end example

@noindent
at the top of the @code{.ly} file.

@warning{Windows users must use double quotes instead of single quotes.}

@cindex output, format
@cindex format, output

@item -f, --format=@var{format}
which formats should be written.  Choices for @code{format} are
@code{ps}, @code{pdf}, and @code{png}.

Example: @code{lilypond -fpng @var{filename}.ly}

@item -h, --help
Show a summary of usage.

@item -H, --header=@var{FIELD}
Dump a header field to file @file{BASENAME.@var{FIELD}}.

@item -i, --init=@var{file}
Set init file to @var{file} (default: @file{init.ly}).

@cindex file searching
@cindex search path

@item -I, --include=@var{directory}
Add @var{directory} to the search path for input files.

Multiple -I options may be given.  The search will start in the first
defined directory, and if the file to be included is not found the
search will continue in subsequent directories.

@cindex chroot jail, running inside

@item -j, --jail=@var{user},@var{group},@var{jail},@var{dir}
Run @command{lilypond} in a chroot jail.

The @option{--jail} option provides a more flexible alternative to
@option{-dsafe}, when LilyPond formatting is being provided via a web
server, or whenever LilyPond executes commands sent by external sources
(see @ref{Advanced command line options for LilyPond}).

It works by changing the root of @command{lilypond} to @var{jail} just
before starting the actual compilation process.  The user and group are
then changed to match those provided, and the current directory is
changed to @var{dir}.  This setup guarantees that it is not possible (at
least in theory) to escape from the jail.  Note that for @option{--jail}
to work, @command{lilypond} must be run as root, which is usually
accomplished in a safe way using @command{sudo}.

Setting up a jail can be a relatively complex matter, as we must be sure
that LilyPond is able to find whatever it needs to compile the source
@emph{inside} the jail itself.  A typical chroot jail will comprise the
following steps:

@table @asis

@item Setting up a separate filesystem
A separate filesystem should be created for LilyPond, so that it can be
mounted with safe options such as @code{noexec}, @code{nodev}, and
@code{nosuid}.  In this way, it is impossible to run executables or to
write directly to a device from LilyPond.  If you do not want to create a
separate partition, just create a file of reasonable size and use it to
mount a loop device.  A separate filesystem also guarantees that LilyPond
cannot write more space than it is allowed.

@item Setting up a separate user
A separate user and group (say, @code{lily}/@code{lily}) with low
privileges should be used to run LilyPond inside the jail.  There should
be a single directory writable by this user, which should be passed in
@var{dir}.

@item Preparing the jail
LilyPond needs to read a number of files while running.  All these files
are to be copied into the jail, under the same path they appear in the
real root filesystem.  The entire content of the LilyPond installation
(e.g., @file{/usr/share/lilypond}) should be copied.

If problems arise, the simplest way to trace them down is to run
LilyPond using @command{strace}, which will allow you to determine which
files are missing.

@item Running LilyPond
In a jail mounted with @code{noexec} it is impossible to execute any
external program.  Therefore LilyPond must be run with a backend that
does not require any such program.  As we have already mentioned, it
must be run with superuser privileges (which, of course, it will lose
immediately), possibly using @command{sudo}.  It is also good practice
to limit the number of seconds of CPU time LilyPond can use (e.g., using
@command{ulimit@tie{}-t}), and, if your operating system supports it,
the amount of memory that can be allocated.  Also see
@ref{LilyPond in chroot jail}.
@end table

@cindex loglevel
@cindex output, verbosity

@item -l, --loglevel=@var{LEVEL}
Set the verbosity of the console output to @var{LEVEL}. Possible values
are:

@table @code

@item NONE
No output at all, not even error messages.

@item ERROR
Only error messages, no warnings or progress messages.

@item WARN
Warnings and error messages, no progress.

@item BASIC_PROGRESS
Basic progress messages (success), warnings and errors.

@item PROGRESS
All progress messages, warnings and errors.

@item INFO (default)
Progress messages, warnings, errors and further execution information.

@item DEBUG
All possible messages, including verbose debug output.

@end table

@cindex directory, redirect output
@cindex output, setting filename
@cindex output, directory

@item -o, --output=@var{FILE} or @var{FOLDER}
Set the default output file to @var{FILE} or, if a folder with that name
exists, direct the output to @var{FOLDER}, taking the file name from the
input file.  The appropriate suffix will be added (e.g. @code{.pdf} for
pdf) in both cases.

@cindex PS (Postscript), output
@cindex Postscript (PS), output
@cindex output, PS (Postscript)

@item --ps
Generate PostScript.

@cindex PNG (Portable Network Graphics), output
@cindex output, PNG (Portable Network Graphics)

@item --png
Generate pictures of each page, in PNG format.  This implies
@option{--ps}.  The resolution in DPI of the image may be set with
@example
-dresolution=110
@end example

@cindex PDF (Portable Document Format), output
@cindex output, PDF (Portable Document Format)

@item --pdf
Generate PDF.  This implies @option{--ps}.

@item -v, --version
Show version information.

@item -V, --verbose
Be verbose: show full paths of all files read, and give timing
information.

@item -w, --warranty
Show the warranty with which GNU LilyPond comes.  (It comes with
@strong{NO WARRANTY}!)

@end table


@node Advanced command line options for LilyPond
@unnumberedsubsec Advanced command line options for LilyPond

@table @code

@item -d@var{[option-name]}=@var{[value]},--define-default=@var{[option-name]}=@var{[value]}
This sets the equivalent internal Scheme function to @var{value}.

@example
-dbackend=svg
@end example

If a @var{value} is not supplied, then the default value is used.  The
prefix @code{no-} may be added to @var{option-name} to switch @q{off} an
option, e.g.

@cindex point and click, command line

@example
-dpoint-and-click=#f
@end example

@noindent
is the same as
@example
-dno-point-and-click
@end example
@end table

@noindent The following are supported along with their respective
default values:

@multitable @columnfractions .33 .16 .51
@item @strong{Symbol}
@tab @strong{Value}
@tab @strong{Explanation/Options}

@item @code{anti-alias-factor}
@tab @code{1}
@tab Render at higher resolution (using given factor) and scale down
result to prevent @q{jaggies} in @code{PNG} images.

@item @code{aux-files}
@tab @code{#t}
@tab Create @code{.tex}, @code{.texi}, @code{.count} files in the
@code{EPS} backend.

@item @code{backend}
@tab @code{ps}
@tab Select backend.  Postscript files (default) include @code{TTF},
@code{Type1} and @code{OTF} fonts.  No subsetting of these fonts is
done.  Using @q{oriental} character sets can lead to very large files.

@item
@tab @code{eps}
@tab Encapsulated PostScript.  This dumps every page (system) as a
separate @file{EPS} file, without fonts, and as one collated @file{EPS}
file with all pages (systems) including fonts.  Used as default by
@command{lilypond-book}.

@item
@tab @code{null}
@tab Do not output a printed score; has the same effect as
@code{-dno-print-pages}.

@item
@tab @code{svg}
@tab Scalable Vector Graphics.  This creates a single SVG file,
without embedded fonts, for every page of output.  It is recommended to
install the Century Schoolbook fonts, included with your LilyPond
installation, for optimal rendering.  Under UNIX, simply copy these
fonts from the LilyPond directory (typically
@file{/usr/share/lilypond/VERSION/fonts/otf/}) to @file{~/.fonts/}.
There is also an option @code{svg-woff} (below) for use of woff font
files in the SVG backend.

@item
@tab @code{scm}
@tab Dump of the raw, internal Scheme-based drawing commands.

@item @code{check-internal-types}
@tab @code{#f}
@tab Check every property assignment for types.

@item @code{clip-systems}
@tab @code{#f}
@tab Generate cut-out snippets of a score.

@item @code{datadir}
@tab
@tab Prefix for data files (read-only).

@item @code{debug-gc}
@tab @code{#f}
@tab Dump memory debugging statistics.

@item @code{debug-gc-assert-parsed-dead}
@tab @code{#f}
@tab For memory debugging: Ensure that all references to parsed objects
are dead. This is an internal option, and is switched on automatically
for @code{`-ddebug-gc'}.

@item @code{debug-lexer}
@tab @code{#f}
@tab Debug the flex lexer.

@item @code{debug-page-breaking-scoring}
@tab @code{#f}
@tab Dump scores for many different page breaking configurations.

@item @code{debug-parser}
@tab @code{#f}
@tab Debug the bison parser.

@item @code{debug-property-callbacks}
@tab @code{#f}
@tab Debug cyclic callback chains.

@item @code{debug-skylines}
@tab @code{#f}
@tab Debug skylines.

@item @code{delete-intermediate-files}
@tab @code{#t}
@tab Delete the unusable, intermediate @code{.ps} files created during
compilation.

@item @code{dump-cpu-profile}
@tab @code{#f}
@tab Dump timing information (system-dependent).

@item @code{dump-profile}
@tab @code{#f}
@tab Dump memory and time information for each file.

@item @code{dump-signatures}
@tab @code{#f}
@tab Dump output signatures of each system. Used for regression testing.

@item @code{eps-box-padding}
@tab @code{#f}
@tab Pad left edge of the output EPS bounding box by the given amount
(in mm).

@item @code{gs-load-fonts}
@tab @code{#f}
@tab Load fonts via Ghostscript.

@item @code{gs-load-lily-fonts}
@tab @code{#f}
@tab Load only the LilyPond fonts via Ghostscript.

@item @code{gui}
@tab @code{#f}
@tab Runs silently and redirect all output to a log file.
@end multitable

@noindent
@strong{Note to Windows users:} By default @code{lilypond.exe} outputs
all progress information to the command window,
@code{lilypond-windows.exe} does not and returns a prompt, with no
progress information, immediately at the command line.  The
@option{-dgui} option can be used in this case to redirect output to a
log file.

@multitable @columnfractions .33 .16 .51
@item @code{help}
@tab @code{#f}
@tab Show this help.

@item @code{include-book-title-preview}
@tab @code{#t}
@tab Include book titles in preview images.

@item @code{include-eps-fonts}
@tab @code{#t}
@tab Include fonts in separate-system EPS files.

@item @code{include-settings}
@tab @code{#f}
@tab Include file for global settings, this is included before the score
is processed.

@item @code{job-count}
@tab @code{#f}
@tab Process in parallel, using the given number of jobs.

@item @code{log-file}
@tab @code{#f [file]}
@tab If string @code{FOO} is given as a second argument,
redirect output to the log file @code{FOO.log}.

@item @code{max-markup-depth}
@tab @code{1024}
@tab Maximum depth for the markup tree. If a markup has more levels,
assume it will not terminate on its own, print a warning and return a
null markup instead.

@item @code{midi-extension}
@tab @code{"midi"}
@tab Set the default file extension for MIDI output file to given
string.

@item @code{music-strings-to-paths}
@tab @code{#f}
@tab Convert text strings to paths when glyphs belong to a music font.

@item @code{paper-size}
@tab @code{\"a4\"}
@tab Set default paper size.  Note the string must be enclosed in
escaped double quotes.

@item @code{pixmap-format}
@tab @code{png16m}
@tab Set GhostScript's output format for pixel images.

@item @code{point-and-click}
@tab @code{#t}
@tab Add @q{point & click} links to PDF and SVG output.
See @ref{Point and click}.

@item @code{preview}
@tab @code{#f}
@tab Create preview images in addition to normal output.
@end multitable

@noindent
This option is supported by all backends; @code{pdf}, @code{png},
@code{ps}, @code{eps} and @code{svg}, but not @code{scm}.  It generates
an output file, in the form @code{myFile.preview.extension}, containing
the titles and the first system of music.  If @code{\book} or
@code{\bookpart} blocks are used, the titles of @code{\book},
@code{\bookpart} or @code{\score} will appear in the output, including
the first system of every @code{\score} block if the @code{\paper}
variable @code{print-all-headers} is set to @code{#t}.

To suppress the usual output, use the @option{-dprint-pages} or
@option{-dno-print-pages} options according to your requirements.

@multitable @columnfractions .33 .16 .51
@item @code{print-pages}
@tab @code{#t}
@tab Generate full pages, the default.  @option{-dno-print-pages} is
useful in combination with @option{-dpreview}.

@item @code{profile-property-accesses}
@tab @code{#f}
@tab Keep statistics of @code{get_property()} function calls.

@item @code{protected-scheme-parsing}
@tab @code{#t}
@tab Continue when errors in inline scheme are caught in the parser. If
set to @code{#f}, halt on errors and print a stack trace.

@item @code{read-file-list}
@tab @code{#f [file]}
@tab Specify name of a file which contains a list of input files to be
processed.

@item @code{relative-includes}
@tab @code{#f}
@tab When processing an @code{\include} command, look for the included
file relative to the current file (instead of the root file).

@item @code{resolution}
@tab @code{101}
@tab Set resolution for generating @code{PNG} pixmaps to given value (in
dpi).

@item @code{safe}
@tab @code{#f}
@tab Do not trust the @code{.ly} input.
@end multitable

@noindent
When LilyPond formatting is available through a web server, either the
@option{--safe} or the @option{--jail} option @b{MUST} be passed.  The
@option{--safe} option will prevent inline Scheme code from wreaking
havoc, e.g,

@quotation
@verbatim
#(s ystem "rm -rf /")  % too dangerous to write correctly
{
  c4^$(ly:gulp-file "/etc/passwd") % malicious but not destructive
}
@end verbatim
@end quotation

The @option{-dsafe} option works by evaluating in-line Scheme
expressions in a special safe module.  This is derived from GUILE
@file{safe-r5rs} module, but also adds a number of functions of the
LilyPond API which are listed in @file{scm/safe-lily.scm}.

In addition, safe mode disallows @code{\include} directives and
disables the use of backslashes in @TeX{} strings.  It is also not
possible to import LilyPond variables into Scheme while in safe mode.

@option{-dsafe} does @emph{not} detect resource overuse, so it is still
possible to make the program hang indefinitely, for example by feeding
cyclic data structures into the backend.  Therefore, if using LilyPond
on a publicly accessible webserver, the process should be limited in
both CPU and memory usage.

Safe mode will prevent many useful LilyPond snippets from being
compiled.

The @option{--jail} is an even more secure alternative, but requires
more work to set up. See @ref{Basic command line options for LilyPond}.

@multitable @columnfractions .33 .16 .51
@item @code{separate-log-files}
@tab @code{#f}
@tab For input files @code{FILE1.ly}, @code{FILE2.ly}, etc. output log
data to files @code{FILE1.log}, @code{FILE2.log}@dots{}

@item @code{show-available-fonts}
@tab @code{#f}
@tab List available font names.

@item @code{strict-infinity-checking}
@tab @code{#f}
@tab Force a crash on encountering @code{Inf} and @code{NaN} floating
point exceptions.

@item @code{strip-output-dir}
@tab @code{#t}
@tab Don't use directories from input files while constructing output
file names.

@item @code{strokeadjust}
@tab @code{#f}
@tab Force PostScript stroke adjustment.  This option is mostly
relevant when a PDF is generated from PostScript output (stroke
adjustment is usually enabled automatically for low-resolution bitmap
devices).  Without this option, PDF previewers tend to produce widely
inconsistent stem widths at resolutions typical for screen display.  The
option does not noticeably affect print quality and causes large file
size increases in PDF files.

@item @code{svg-woff}
@tab @code{#f}
@tab Use woff font files in SVG backend.

@item @code{trace-memory-frequency}
@tab @code{#f}
@tab Record Scheme cell usage this many times per second.  Dump the
results to @code{FILE.stacks} and @code{FILE.graph}.

@item @code{trace-scheme-coverage}
@tab @code{#f}
@tab Record coverage of Scheme files in @code{FILE.cov}.

@item @code{verbose}
@tab @code{#f}
@tab Verbose output, i.e. loglevel at DEBUG (read-only).

@item @code{warning-as-error}
@tab @code{#f}
@tab Change all warning and @q{programming error} messages into errors.
@end multitable


@node Environment variables
@unnumberedsubsec Environment variables

@cindex LANG
@cindex LILYPOND_DATADIR

@command{lilypond} recognizes the following environment variables:
@table @code
@item LILYPOND_DATADIR
This specifies a directory where locale messages and
data files will be looked up by default.  The directory should contain
subdirectories called @file{ly/}, @file{ps/}, @file{tex/}, etc.

@item LANG
This selects the language for the warning messages.

@item LILYPOND_LOGLEVEL
The default loglevel. If LilyPond is called without an explicit loglevel
(i.e. no @option{--loglevel} command line option), this value is used.

@item LILYPOND_GC_YIELD
A variable, as a percentage, that tunes memory management
behavior.  A higher values means the program uses more memory, a
smaller value means more CPU time is used.  The default value is
@code{70}.

@end table


@node LilyPond in chroot jail
@unnumberedsubsec LilyPond in chroot jail

Setting up the server to run LilyPond in a chroot jail is a complicated
task.  The steps are listed below.  Examples in the steps are from
Ubuntu GNU/Linux, and may require the use of @code{sudo} as appropriate.

@itemize

@item Install the necessary packages: LilyPond, GhostScript, and ImageMagick.

@item Create a new user by the name of @code{lily}:

@example
adduser lily
@end example

@noindent
This will create a new group for the @code{lily} user as well, and a
home folder, @code{/home/lily}

@item In the home folder of the @code{lily} user create a file to use as a
separate filesystem:

@example
dd if=/dev/zero of=/home/lily/loopfile bs=1k count= 200000
@end example

@noindent
This example creates a 200MB file for use as the jail filesystem.

@item Create a loop device, make a file system and mount it, then create
a folder that can be written by the @code{lily} user:

@example
mkdir /mnt/lilyloop
losetup /dev/loop0 /home/lily/loopfile
mkfs -t ext3 /dev/loop0 200000
mount -t ext3 /dev/loop0 /mnt/lilyloop
mkdir /mnt/lilyloop/lilyhome
chown lily /mnt/lilyloop/lilyhome
@end example

@item In the configuration of the servers, the JAIL will be @code{/mnt/lilyloop}
and the DIR will be @code{/lilyhome}.

@item Create a big directory tree in the jail by copying the necessary files, as
shown in the sample script below.

You can use @code{sed} to create the necessary copy commands for a given
executable:

@example
for i in "/usr/local/lilypond/usr/bin/lilypond" "/bin/sh" "/usr/bin/;  \
  do ldd $i | sed 's/.*=> \/\(.*\/\)\([^(]*\).*/mkdir -p \1 \&\&  \
    cp -L \/\1\2 \1\2/' | sed 's/\t\/\(.*\/\)\(.*\) (.*)$/mkdir -p  \
      \1 \&\& cp -L \/\1\2 \1\2/' | sed '/.*=>.*/d'; done
@end example

@end itemize

@subheading Example script for 32-bit Ubuntu 8.04

@example
#!/bin/sh
## defaults set here

username=lily
home=/home
loopdevice=/dev/loop0
jaildir=/mnt/lilyloop
# the prefix (without the leading slash!)
lilyprefix=usr/local
# the directory where lilypond is installed on the system
lilydir=/$lilyprefix/lilypond/

userhome=$home/$username
loopfile=$userhome/loopfile
adduser $username
dd if=/dev/zero of=$loopfile bs=1k count=200000
mkdir $jaildir
losetup $loopdevice $loopfile
mkfs -t ext3 $loopdevice 200000
mount -t ext3 $loopdevice $jaildir
mkdir $jaildir/lilyhome
chown $username $jaildir/lilyhome
cd $jaildir

mkdir -p bin usr/bin usr/share usr/lib usr/share/fonts $lilyprefix tmp
chmod a+w tmp

cp -r -L $lilydir $lilyprefix
cp -L /bin/sh /bin/rm bin
cp -L /usr/bin/convert /usr/bin/gs usr/bin
cp -L /usr/share/fonts/truetype usr/share/fonts

# Now the library copying magic
for i in "$lilydir/usr/bin/lilypond" "$lilydir/usr/bin/guile" "/bin/sh"  \
  "/bin/rm" "/usr/bin/gs" "/usr/bin/convert"; do ldd $i | sed 's/.*=>  \
    \/\(.*\/\)\([^(]*\).*/mkdir -p \1 \&\& cp -L \/\1\2 \1\2/' | sed  \
      's/\t\/\(.*\/\)\(.*\) (.*)$/mkdir -p \1 \&\& cp -L \/\1\2 \1\2/'  \
        | sed '/.*=>.*/d'; done | sh -s

# The shared files for ghostscript...
      cp -L -r /usr/share/ghostscript usr/share
# The shared files for ImageMagick
      cp -L -r /usr/lib/ImageMagick* usr/lib

### Now, assuming that you have test.ly in /mnt/lilyloop/lilyhome,
### you should be able to run:
### Note that /$lilyprefix/bin/lilypond is a script, which sets the
### LD_LIBRARY_PATH - this is crucial
      /$lilyprefix/bin/lilypond -jlily,lily,/mnt/lilyloop,/lilyhome test.ly
@end example

@c " keep quote signs balanced for context-sensitive editors

@node Error messages
@section Error messages

@cindex error messages
Different error messages can appear while compiling a file:

@table @emph

@item Warning
@cindex warning
Something looks suspect.  If you are requesting something out of the
ordinary then you will understand the message, and can ignore it.
However, warnings usually indicate that something is wrong with the
input file.

@item Error
@cindex error
Something is definitely wrong.  The current processing step (parsing,
interpreting, or formatting) will be finished, but the next step will
be skipped.

@item Fatal error
@cindex fatal error
Something is definitely wrong, and LilyPond cannot continue.  This
happens rarely.  The most usual cause is misinstalled fonts.

@item Scheme error
@cindex trace, Scheme
@cindex call trace
@cindex Scheme error
Errors that occur while executing Scheme code are caught by the Scheme
interpreter.  If running with the verbose option (@option{-V} or
@option{--verbose}) then a call trace of the offending
function call is printed.

@item Programming error
@cindex Programming error
There was some internal inconsistency.  These error messages are
intended to help the programmers and debuggers.  Usually, they can be
ignored.  Sometimes, they come in such big quantities that they obscure
other output.

@item Aborted (core dumped)
@cindex Aborted (core dumped)
This signals a serious programming error that caused the program to
crash.  Such errors are considered critical.  If you stumble on one,
send a bug-report.
@end table

@cindex errors, message format
If warnings and errors can be linked to some part of the input file,
then error messages have the following form

@example
@var{filename}:@var{lineno}:@var{columnno}: @var{message}
@var{offending input line}
@end example

A line-break is inserted in the offending line to indicate the column
where the error was found.  For example,

@example
test.ly:2:19: error: not a duration: 5
  @{ c'4 e'
           5 g' @}
@end example

These locations are LilyPond's best guess about where the warning or
error occurred, but (by their very nature) warnings and errors occur
when something unexpected happens.  If you can't see an error in the
indicated line of your input file, try checking one or two lines
above the indicated position.

Please note that diagnostics can be triggered at any point during the
many stages of processing.  For example if there are parts of the input
that are processed multiple times (i.e. in midi and layout output), or
if the same music variable is used in multiple contexts the same message
may appear several times.  Diagnostics produced at a @q{late} stage (i.e
bar checks) might also be issued multiple times.

More information about errors is given in @ref{Common errors}.


@node Common errors
@section Common errors

The error conditions described below occur often, yet the cause
is not obvious or easily found.  Once seen and understood, they
are easily handled.


@menu
* Music runs off the page::
* An extra staff appears::
* Error message Unbound variable %::
* Error message FT_Get_Glyph_Name::
* Warning staff affinities should only decrease::
* Error message unexpected new::
* Warning ignoring too many clashing note columns::
@end menu

@node Music runs off the page
@unnumberedsubsec Music runs off the page

Music running off the page over the right margin or appearing
unduly compressed is almost always due to entering an incorrect
duration on a note, causing the final note in a measure to extend
over the bar line.  It is not invalid if the final note in a
measure does not end on the automatically entered bar line, as the
note is simply assumed to carry over into the next measure.  But
if a long sequence of such carry-over measures occurs the music
can appear compressed or may flow off the page because automatic
line breaks can be inserted only at the end of complete measures,
i.e., where all notes end before or at the end of the measure.

@warning{An incorrect duration can cause line breaks to be
inhibited, leading to a line of highly compressed music or
music which flows off the page.}

The incorrect duration can be found easily if bar checks are used,
see @ruser{Bar and bar number checks}.

If you actually intend to have a series of such carry-over measures
you will need to insert an invisible bar line where you want the
line to break.  For details, see @ruser{Bar lines}.


@node An extra staff appears
@unnumberedsubsec An extra staff appears

If contexts are not created explicitly with @code{\new} or
@code{\context}, they will be silently created as soon as a
command is encountered which cannot be applied to an existing
context.  In simple scores the automatic creation of contexts is
useful, and most of the examples in the LilyPond manuals take
advantage of this simplification.  But occasionally the silent
creation of contexts can give rise to unexpected new staves or
scores.  For example, it might be expected that the following code
would cause all note heads within the following staff to be
colored red, but in fact it results in two staves with the note
heads remaining the default black in the lower staff.

@lilypond[quote,verbatim,relative=2]
\override Staff.NoteHead.color = #red
\new Staff { a }
@end lilypond

This is because a @code{Staff} context does not exist when the
override is processed, so one is implicitly created and the override
is applied to it, but then the @code{\new Staff} command creates
another, separate, staff into which the notes are placed.  The
correct code to color all note heads red is

@lilypond[quote,verbatim,relative=2]
\new Staff {
  \override Staff.NoteHead.color = #red
  a
}
@end lilypond

@node Error message Unbound variable %
@unnumberedsubsec Error message Unbound variable %

This error message will appear at the bottom of the console
output or log file together with a @qq{GUILE signalled an error @dots{}}
message every time a Scheme routine is called which (invalidly)
contains a @emph{LilyPond} rather than a @emph{Scheme} comment.

LilyPond comments begin with a percent sign, (@code{%}), and must
not be used within Scheme routines.  Scheme comments begin with a
semi-colon, (@code{;}).

@node Error message FT_Get_Glyph_Name
@unnumberedsubsec Error message FT_Get_Glyph_Name

This error messages appears in the console output or log file if
an input file contains a non-ASCII character and was not saved in
UTF-8 encoding.  For details, see @ruser{Text encoding}.


@node Warning staff affinities should only decrease
@unnumberedsubsec Warning staff affinities should only decrease

This warning can appear if there are no staves in the printed
output, for example if there are just a @code{ChordName} context
and a @code{Lyrics} context as in a lead sheet.  The warning
messages can be avoided by making one of the contexts behave as a
staff by inserting

@example
\override VerticalAxisGroup.staff-affinity = ##f
@end example

@noindent
at its start.  For details, see @qq{Spacing of non-staff lines} in
@ruser{Flexible vertical spacing within systems}.


@node Error message unexpected new
@unnumberedsubsec Error message unexpected @code{@bs{}new}

A @code{\score} block must contain a @emph{single} music expression.
If instead it contains several @code{\new Staff},
@code{\new StaffGroup} or similar contexts introduced with @code{\new}
without them being enclosed in either curly brackets,
@code{@{ @dots{} @}}, or double angle brackets, @code{<< @dots{} >>},
like this:

@example
\score @{
  % Invalid! Generates error: syntax error, unexpected \new
  \new Staff @{ @dots{} @}
  \new Staff @{ @dots{} @}
@}
@end example

@noindent
the error message will be produced.

To avoid the error, enclose all the @code{\new} statements in
curly or double angle brackets.

Using curly brackets will introduce the @code{\new} statements
sequentially:

@lilypond[quote,verbatim]
\score {
  {
    \new Staff { a' a' a' a' }
    \new Staff { g' g' g' g' }
  }
}
@end lilypond

@noindent
but more likely you should be using double angle brackets so the new
staves are introduced in parallel, i.e. simultaneously:

@lilypond[quote,verbatim]
\score {
  <<
    \new Staff { a' a' a' a' }
    \new Staff { g' g' g' g' }
  >>
}
@end lilypond

@node Warning ignoring too many clashing note columns
@unnumberedsubsec Warning ignoring too many clashing note columns

If notes from two different voices with stems in the same direction
occur at the same musical moment, but the voices have no
voice-specific shifts specified, the warning message
@samp{warning: ignoring too many clashing note columns} will appear
when compiling the LilyPond file.  This warning will appear even when
the notes have no visible stems, e.g. whole notes, if the stems for
shorter notes at the same pitch would be in the same direction.

Remember that the stem direction depends on the position of the
note on the staff unless the stem direction is specified, for example
by using @code{\voiceOne}, etc.  In this case the warning will appear
only when the stems happen to be in the same direction, i.e. when the
notes are in the same half of the staff.

By placing the notes in voices with stem directions and shifts
specified, for example by using @code{\voiceOne}, etc., these warnings
may be avoided.

Notes in higher numbered voices, @code{\voiceThree} etc., are
automatically shifted to avoid clashing note columns.  This causes a
visible shift for notes with stems, but whole notes are not visibly
shifted unless an actual clash of the note heads occurs, or when the
voices cross over from their natural order (when @code{\voiceThree}
is higher than @code{\voiceOne}, etc.)

@seealso
@rlearning{Explicitly instantiating voices},
@rlearning{Real music example},
@ruser{Single-staff polyphony},
@ruser{Collision resolution}.