SAO DS9 (GNU Astronomy Utilities)

B.1 SAO DS9

SAO DS9 is not a requirement of Gnuastro, it is a FITS image viewer. It is therefore a useful tool to visually inspect the images/cubes of your Gnuastro inputs or outputs (for tables, see TOPCAT). In Gnuastro we have an installed script to run DS9 or TOPCAT on any number of FITS files (depending on it being an image or table), see Viewing FITS file contents with DS9 or TOPCAT (which also includes a .desktop file for GUI integration). After installing DS9, you can easily use that script to open any FITS file (table, image or cube).

Like the other packages, it might already be available in your distribution’s repositories. It is also already pre-compiled in the download section of its web page. Once you download it you can unpack and install (move it to a system recognized directory) with the following commands (x.x.x is the version number):

$ tar xf ds9.linux64.x.x.x.tar.gz
$ sudo mv ds9 /usr/local/bin

To test the build (as long as /usr/local/bin is in your PATH, see Installation directory), you can simply run the command below.

$ ds9

Install without root permissions: If you don’t have root permissions, you can simply replace /usr/local/bin in the command above with $HOME/.local/bin. If this directory isn’t in your PATH, you can simply add it with the command below (in your startup file, e.g., ~/.bashrc). For more on PATH and the startup files, see Installation directory.

export PATH="$HOME/.local/bin:$PATH"

Below you can see a list of known issues in some operating systems that we have found so far. You should be able to identify any potential error when running DS9 from the command-line like above.

There might be a complaint about the Xss library, which you can find in your distribution package management system.
You might also get an XPA related error. In this case, you have to add the following line to your ~/.bashrc and ~/.profile file (you will have to log out and back in again for the latter):
```
export XPA_METHOD=local
```
Your system may not have the SSL library in its standard library path, in this case, put this command in your startup file (for example ~/.bashrc):
```
export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:/usr/local/ssl/lib"
```