trick applications to use different $HOME

scrawl · 2011-11-26 00:11:22

My problem: I play games a lot and want to sync my savegames and settings between laptop and pc.

This is my approach: I have a launch script that every game gets run with. This launch script changes the $HOME environment variable to a special "Savegames" folder in my home directory, now I can just sync this whole folder.

This works fine with most games I've tried until now. However there is one (Prey) that still puts the savegames in $HOME/.prey instead of $HOME/Savegames/.prey !

So, essentially, my question is: What's the best way to trick a program that I have a different home directory?

ewaller · 2011-11-26 00:58:39

You might try creating ~/Savegames/.prey and then make a softlink :
ln -s ~/Savegames/.prey ~/.prey

Note that that won't work if ~/.prey already exists. You may want to create ~/Savegames/.prey by moving ~/.prey the the Savegames directory

.:B:. · 2011-11-26 06:43:08

Probably by setting the XDG_CONFIG_HOME variable for your game specifically.

scrawl · 2011-11-26 12:55:42

ewaller wrote:

You might try creating ~/Savegames/.prey and then make a softlink :
ln -s ~/Savegames/.prey ~/.prey

I already considered that, the drawback is that I have to tell the script the save game folder for every game, which I don't really want to do...

.:B:. wrote:

Probably by setting the XDG_CONFIG_HOME variable for your game specifically.

I've now literally set every XDG_* and any other environment variable that had my login name in it. Still the game finds out about my real home folder.

ewaller · 2011-11-26 17:07:17

You can always edit the source

scrawl · 2011-11-26 19:04:09

Not for commercial games... wish I could

I guess I'll go for the symlink way then, even if its stupid...

Last edited by scrawl (2011-11-26 19:04:37)

SlayingDragons · 2011-11-27 02:31:37

While the symlink way is probably the best way to do it, if you want to change your home directory in the bash session you're in, you can enter:

export HOME=/home/*user*/Savegames/.prey

Which if you're launching the game from a terminal should make it recognize it as your home folder.

putte_xvi · 2011-11-27 23:32:49

It could be reading the home directory using the getpwnam(3) function, or directly from /etc/passwd. You can probably find out by running something like:

ltrace -e getpwnam,getpwuid,getpwnam_r,getpwuid_r my_prey_executable >/dev/null

If this is the case, given that we don't have the source, maybe one could write a library with a fake version of the appropriate function and set LD_PRELOAD to make the game use it?

Or maybe it's simply writing stuff to the current directory and you just happen to always launch it from your home directory.

If all else fails, you could run the games as a separate user (using su or sudo) and treat that user's home folder as the savegames folder.

scrawl · 2011-11-28 00:00:16

ltrace -e getpwnam,getpwuid,getpwnam_r,getpwuid_r ./prey.x86 >/dev/null
getpwuid(1000, 0xf73c22a0, 1, 0, 0x84fb520)      = 0xf7577c70
getpwuid(1000, 0, 248144, -1, -1)                = 0xf7577c70

If this is the case, given that we don't have the source, maybe one could write a library with a fake version of the appropriate function and set LD_PRELOAD to make the game use it?

Sounds like overkill

Last edited by scrawl (2011-11-28 00:00:26)

putte_xvi · 2011-11-28 01:26:49

scrawl wrote:

ltrace -e getpwnam,getpwuid,getpwnam_r,getpwuid_r ./prey.x86 >/dev/null
getpwuid(1000, 0xf73c22a0, 1, 0, 0x84fb520)      = 0xf7577c70
getpwuid(1000, 0, 248144, -1, -1)                = 0xf7577c70
If this is the case, given that we don't have the source, maybe one could write a library with a fake version of the appropriate function and set LD_PRELOAD to make the game use it?
Sounds like overkill

Well, I decided to give it a try. I'm not really a C programmer, but it was actually much easier than expected. This was quite helpful: http://www.technovelty.org/code/c/override.html

Save the code below as libfakehome.c and change the path (FAKE_HOMEDIR) to what you want:

#define FAKE_HOMEDIR "/opt/games"
#define FAKE_HOMEDIR_UID 1000

#define _GNU_SOURCE 1
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <pwd.h>
#include <dlfcn.h>

struct passwd *getpwuid(uid_t uid) {
    static struct passwd fake;
    struct passwd *(*real_getpwuid)(uid_t) = dlsym(RTLD_NEXT, "getpwuid");
    struct passwd *pwentry;
    pwentry = real_getpwuid(uid);
    if (uid != FAKE_HOMEDIR_UID) {
        return pwentry;
    }
    if (pwentry == NULL) {
        fprintf(stderr, "Failed to fake home directory.\n");
        return NULL;
    }
    fake = *pwentry;
    fake.pw_dir = FAKE_HOMEDIR;
    fprintf(stderr, "Faking home directory: %s\n", fake.pw_dir);
    return &fake;
}

Compile it:

gcc -shared -fPIC -ldl -o /somewhere/libfakehome.so libfakehome.c

And run it:

LD_PRELOAD=/somewhere/libfakehome.so ./prey.x86

scrawl · 2011-11-28 16:02:16

Wow, that looks really cool!

How would I compile it for x86 (Since I'm running 64 bit arch, but prey is 32 bit)?

Edit: Solved: install gcc-multilib and compile with -m32 flag.

and it just works Thank you very much

Maybe I will release something when I'm finished. I'm doing a collection of scripts to make installing/running games across multiple linuxes easier (Current features are shared savegame folder, and script to launch on different XServer for games that don't allow you to tab out - in the future maybe also wine support and a game database ala playonlinux)

Last edited by scrawl (2011-11-28 16:09:51)

Arch Linux

#1 2011-11-26 00:11:22

trick applications to use different $HOME

#2 2011-11-26 00:58:39

Re: trick applications to use different $HOME

#3 2011-11-26 06:43:08

Re: trick applications to use different $HOME

#4 2011-11-26 12:55:42

Re: trick applications to use different $HOME

#5 2011-11-26 17:07:17

Re: trick applications to use different $HOME

#6 2011-11-26 19:04:09

Re: trick applications to use different $HOME

#7 2011-11-27 02:31:37

Re: trick applications to use different $HOME

#8 2011-11-27 23:32:49

Re: trick applications to use different $HOME

#9 2011-11-28 00:00:16

Re: trick applications to use different $HOME

#10 2011-11-28 01:26:49

Re: trick applications to use different $HOME

#11 2011-11-28 16:02:16

Re: trick applications to use different $HOME

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