This file is indexed.

/usr/share/gmt/dbase/grdraster.info is in gmt-common 5.3.1+dfsg-2.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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#	$Id: grdraster.info 12822 2014-01-31 23:39:56Z remko $
#
# This file contains information on rasterfiles which are readable with grdraster.
# This file must be named grdraster.info.  At run time, grdraster will look for
# this file in $GMT_USERDIR (which defaults to ~/.gmt), $GMT_GRIDDIR, and
# $GMT_SHAREDIR/dbase (in that order).  Any line beginning with a # will be
# treated as a comment, and blank lines are skipped.  Any other line must have
# the following items, all on one line, one line, pertaining to one rasterfile:
#
# file_number "title string" "z units" -R -I GorP type scale offset NaNflag filename [L|B] [H<bytes>]
#
# There must be white space between each item.  "title string" and "z units" must
# be enclosed in " ", and they may have white space within them.  They are limited
# to a maximum of 80 characters.  No other quotation marks should be on a line.
# The entire line should be writable in 320 characters.
#
# file_number is an integer used to tell grdraster which raster to read.  It must
# 	be unique to each raster.
# "title string" is a brief description of the data.
# "z units"  describes the units of the data after they are scaled and offset.
# -R<w>/<e>/<s>/<n> describes the range of the raster in the usual GMT -R manner.
# -I<x_inc>/<y_inc> describes the sampling interval in the usual GMT -I manner.
# GorP is either G or P, indicating Grid or Pixel registration.  Optionally, you
#	can append G (Geographic) or C (Cartesian) to explicitly set this attribute
#	which would otherwise be guessed based on the x/y range
# type is one of the following, indicating the kind of data stored in the raster:
#	b	bit data, either 0 or 1, one bit per data value.
#	u	unsigned character data.
#	c	signed character data.
#	d	unsigned two-byte integer data.
#	i	signed two-byte integer data.
#	l	signed four-byte integer data.
# scale is a number which should be multiplied on the raster value after read.
# offset is a number which should be added to the [scaled] raster value.
# NaNflag is a number which is written in the raster to represent NaN.
#	If all values in the raster represent data, NaNflag is none.
# filename is the name the raster file.  If filename begins with a "/", then
#	it will be treated as a complete name.  If not, we will look for the
#	file in the directories pointed to by $GMT_DATADIR.
#
# BYTE-ORDER:
#
# Optionally, you may append a single character L (for Little-endian) or B (for
# Big-endian) to indicate the endian-ness of this data file.  If the present
# endianness of your computer has a different endianness that specified for the
# chosen data set, then grdraster will automatically swap the bytes.  The
# endianness of your computer is automatically determined at compile-time.
#
# You will need to edit this to reflect which data you have installed on your
# system, and optionally append L or B to indicate endian-ness:
#
# Finally, if your raster grid has a header you can specify the size of the header
# in bytes and grdraster will skip these bytes before reading the data

1 "ETOPO5 global topography"	"m"	-R0/359:55/-90/90	-I5m		GG i 1		0	none	etopo5.i2
2 "US Elevations from USGS"	"m"	-R234/294/24/50		-I0.5m		PG i 0.3048	0	-9999	us_topo30s.i2
3 "Geosat/Seasat gravity from Haxby"	"mGal"	-R0/360/-90/90	-I5m		GG i 0.1	0	none	haxby5m_faa.i2
4 "Geosat/Seasat geoid from Haxby"	"m"	-R0/360/-90/90	-I5m		GG i 0.001	0	none	haxby5m_geoid.i2
5 "Sea floor age from Cande"	"Ma"	-R0/360/-90/90		-I5m		PG i 0.1	0	-30000	cande5m_ages.i2
6 "Sea floor age from Muller"	"Ma"	-R0/360/-72/72		-I6m		GG i 0.01	0	32767	scripps6m_ages.i2
7 "1=land, 0=sea bitmask"	"T/F"	-R0/360/-90/90		-I5m		PG b 1		0	none	landsea.bits
#8 "Seasat geoid from J. Marsh"	"m"	-R0/359.875/-60/70	-I0.125		GG i 0.01	0	32765	marsh.geo
#9 "Geosat gravity from Marks"	"mGal"	-R0/360/-72/-30		-I0.05/0.04	GG i 0.01	0	32767	geosat30.bin
#10 "Seasat gravity from Haxby"	"mGal"	-R0:05/360/-71:55/72	-I5m		GG i 0.1	0	none	haxby.bin