Sage uses several environment variables when running. These all have sensible default values, so many users won’t need to set any of these. (There are also variables used to compile Sage; see the Sage Installation Guide for more about those.)

`DOT_SAGE`– this is the directory, to which the user has read and write access, where Sage stores a number of files. The default location is`~/.sage/`, but you can change that by setting this variable.`SAGE_RC_FILE`– a shell script which is sourced after Sage has determined its environment variables. This script is executed before starting Sage or any of its subcommands (like`sage -i <package>`). The default value is`$DOT_SAGE/sagerc`.`SAGE_STARTUP_FILE`– a file including commands to be executed every time Sage starts. The default value is`$DOT_SAGE/init.sage`.`SAGE_SERVER`– if you want to install a Sage package using`sage -i PKG_NAME`, Sage downloads the file from the web, using the address`http://www.sagemath.org/`by default, or the address given by`SAGE_SERVER`if it is set. If you wish to set up your own server, then note that Sage will search the directories`SAGE_SERVER/packages/standard/`,`SAGE_SERVER/packages/optional/`,`SAGE_SERVER/packages/experimental/`, and`SAGE_SERVER/packages/archive/`for packages. See the script`$SAGE_ROOT/spkg/bin/sage-spkg`for the implementation.`SAGE_PATH`– a colon-separated list of directories which Sage searches when trying to locate Python libraries.`SAGE_BROWSER`– on most platforms, Sage will detect the command to run a web browser, but if this doesn’t seem to work on your machine, set this variable to the appropriate command.`SAGE_ORIG_LD_LIBRARY_PATH_SET`– set this to something non-empty to force Sage to set the`LD_LIBRARY_PATH`before executing system commands.`SAGE_ORIG_DYLD_LIBRARY_PATH_SET`– similar, but only used on Mac OS X to set the`DYLD_LIBRARY_PATH`.`SAGE_CBLAS`– used in the file`SAGE_ROOT/src/sage/misc/cython.py`. Set this to the base name of the BLAS library file on your system if you want to override the default setting. That is, if the relevant file is called`libcblas_new.so`or`libcblas_new.dylib`, then set this to “cblas_new”.