diff --git a/html/inc/db_conn.inc b/html/inc/db_conn.inc
index b39ae8d36f..37605a16e6 100644
--- a/html/inc/db_conn.inc
+++ b/html/inc/db_conn.inc
@@ -116,8 +116,8 @@ class DbConn {
 
     function enum_general($classname, $query) {
         $result = $this->do_query($query);
-        if (!$result) return null;
-        $x = array();
+        if (!$result) return [];
+        $x = [];
         while ($obj = $result->fetch_object($classname)) {
             $x[] = $obj;
         }
@@ -133,7 +133,7 @@ class DbConn {
             $where_clause = "where $where_clause";
         }
         $query = "select $fields from DBNAME.$table $where_clause $order_clause";
-        return $this->enum_general($classname,$query);
+        return $this->enum_general($classname, $query);
     }
 
     function enum($table, $classname, $where_clause=null, $order_clause=null) {
diff --git a/html/inc/dir_hier.inc b/html/inc/dir_hier.inc
index ea898bab91..9f3b54fd04 100644
--- a/html/inc/dir_hier.inc
+++ b/html/inc/dir_hier.inc
@@ -120,9 +120,7 @@ function check_download_file($path, $dl_path) {
     }
 }
 
-// Stage the given file, which is assumed to not be in download dir already.
-//
-function stage_file_basic($dir, $fname) {
+function get_hier_info() {
     static $dl_dir = null;
     static $fanout = null;
     if (!$dl_dir) {
@@ -130,6 +128,13 @@ function stage_file_basic($dir, $fname) {
         $dl_dir = parse_config($conf, "<download_dir>");
         $fanout = parse_config($conf, "<uldl_dir_fanout>");
     }
+    return [$dl_dir, $fanout];
+}
+
+// Stage the given file, which is assumed to not be in download dir already.
+//
+function stage_file_basic($dir, $fname) {
+    [$dl_dir, $fanout] = get_hier_info();
     $old_path = "$dir/$fname";
     $new_path = dir_hier_path($fname, $dl_dir, $fanout);
     $md5 = md5_file($old_path);
@@ -138,4 +143,14 @@ function stage_file_basic($dir, $fname) {
     rename($old_path, $new_path);
 }
 
+// copy the given file (with known size/md5)
+// to the download dir w/ given phys name
+//
+function stage_file_aux($path, $md5, $size, $phys_name) {
+    [$dl_dir, $fanout] = get_hier_info();
+    $phys_path = dir_hier_path($phys_name, $dl_dir, $fanout);
+    copy($path, $phys_path);
+    file_put_contents("$phys_path.md5", "$md5 $size\n");
+}
+
 ?>
diff --git a/html/inc/sandbox.inc b/html/inc/sandbox.inc
index 2746048f43..620c8e4d5a 100644
--- a/html/inc/sandbox.inc
+++ b/html/inc/sandbox.inc
@@ -19,14 +19,23 @@
 // Utility functions for user file sandbox feature
 //
 // In this system:
-// - sandbox files live in the download hierarchy,
-//   with names of the form sb_userid_md5
-// - each user has a "sandbox dir" project/sandbox/userid.
-//   The files in this have user-visible names, and contents of the form
-//   sb file_size file_md5
+// - each user (job submitter) has a 'sandbox' where they can store files
+//      on the BOINC server, via a web interface.
+//      These files are mutable; you can modify a file w/ a given name.
+// - files are stored in a dir project/sandbox/<userid>
+// - When a file is uploaded, its size and MD5 are computed and stored
+//      in an 'info file' in a parallel dir, project/sandbox/<userid>/.md5
+//
+// Sandbox files can be used for web-based job submissions systems
+// like BUDA and autodock on BOINC Central.
+// Typically they are used as job input files or app files,
+// in which case they are downloadable.
+// When a file is used in this way,
+// it must be copied to the download hierarchy,
+// and assigned a physical name that includes its MD5.
+// The name depends on the role of the file.
 
 require_once("../inc/util.inc");
-require_once("../inc/submit_db.inc");
 require_once("../inc/dir_hier.inc");
 
 // Return path of sandbox directory for the given user.
@@ -44,75 +53,53 @@ function sandbox_dir($user) {
     if (!is_dir($d)) {
         mkdir($d);
     }
+    if (!is_dir("$d/.md5")) {
+        mkdir("$d/.md5");
+    }
     return $d;
 }
 
-function sandbox_write_link_file($path, $size, $md5) {
-    file_put_contents($path, "sb $size $md5");
-}
-
-// check if a link with the given md5 exists
+// parse a sandbox file's info file.
+// If missing, create it.
 //
-function sandbox_lf_exists($user, $md5) {
-    $exist = false;
-    $elf = "";
+function sandbox_parse_info_file($user, $name) {
     $dir = sandbox_dir($user);
-    $files = sandbox_file_names($user);
-    foreach ($files as $file) {
-        $path = "$dir/$file";
-        [$err, $file_size, $file_md5] = sandbox_parse_link_file($path);
-        if (!$err){
-            if (strcmp($md5, $file_md5) == 0) {
-                $exist = true;
-                $elf = $file;
-                break;
-            }
-        }
+    $info_path = "$dir/.md5/$name";
+    $info = parse_info_file($info_path);
+    if ($info) {
+        return $info;
     }
-    return array($exist, $elf);
-}
-
-// parse a link file and return (error, size, md5)
-//
-function sandbox_parse_link_file($path) {
-    if (!file_exists($path)) { return array(true, null, null); }
-    $x = file_get_contents($path);
-    $n = sscanf($x, "%s %d %s", $s, $size, $md5);
-    if ($n != 3) return array(true, null, null);
-    if ($s != 'sb') return array(true, null, null);
-    return array(false, $size, $md5);
-}
-
-$fanout = parse_config(get_config(), "<uldl_dir_fanout>");
-
-// return the physical name of the file
-//
-function sandbox_file_name($user, $md5) {
-    return "sb_".$user->id."_".$md5;
-}
-
-// return the path of the file in the download directory
-//
-function sandbox_physical_path($user, $md5) {
-    global $fanout;
-    $f = sandbox_file_name($user, $md5);
-    return dir_hier_path($f, parse_config(get_config(), "<download_dir>"), $fanout);
+    [$size, $md5] = get_file_info("$dir/$name");
+    write_info_file($info_path, $md5, $size);
+    return [$md5, $size];
 }
 
 // return list of files in sandbox
 //
 function sandbox_file_names($user) {
-    $d = opendir(sandbox_dir($user));
+    $files = scandir(sandbox_dir($user));
     $names = array();
-    while (($f = readdir($d)) !== false) {
-        if ($f == '.') continue;
-        if ($f == '..') continue;
+    foreach ($files as $f) {
+        if ($f[0] == '.') continue;
         $names[] = $f;
     }
     natsort($names);
     return $names;
 }
 
+// return list of files matching given pattern,
+// in the format used for form_select() and form_select_multiple()
+//
+function sandbox_select_items($user, $pattern=null) {
+    $sbfiles = sandbox_file_names($user);
+    $sbitems = [];
+    foreach ($sbfiles as $f) {
+        if ($pattern && !preg_match($pattern, $f)) continue;
+        $sbitems[] = [$f, $f];
+    }
+    return $sbitems;
+}
+
 // return a <select> for files in sandbox
 //
 function sandbox_file_select(
@@ -131,66 +118,13 @@ function sandbox_file_select(
     return $x;
 }
 
-// convert sandbox (link) name to physical path
+// copy file and info file from sandbox to $dir
+// (which must have a subdir .md5/)
 //
-function sandbox_log_to_phys($user, $log_name) {
-    $dir = sandbox_dir($user);
-    [$err, $file_size, $file_md5] = sandbox_parse_link_file("$dir/$log_name");
-    if ($err) return null;
-    return sandbox_physical_path($user, $file_md5);
-}
-
-// convert sandbox name to physical name
-//
-function sandbox_name_to_phys_name($user, $log_name) {
-    $dir = sandbox_dir($user);
-    [$err, $file_size, $file_md5] = sandbox_parse_link_file("$dir/$log_name");
-    if ($err) return null;
-    return sandbox_file_name($user, $file_md5);
-}
-
-// check if a file is still being used by a unfinished batch
-//
-// TODO: this is a kludge.
-// Should we use the job_file and batch_file_assoc tables instead?
-//
-function sandbox_file_in_use($user, $file){
-    $ufiles = array();
-
-    $pbatches = BoincBatch::enum(
-        sprintf('user_id=%d and state!=%d and state!=%d',
-            $user->id, BATCH_STATE_COMPLETE, BATCH_STATE_ABORTED
-        )
-    );
-    if (!$pbatches) return false;
-
-    foreach ($pbatches as $batch){
-        $wus = BoincWorkUnit::enum("batch = $batch->id limit 1" );
-        if ($wus == null){
-            continue;
-        }
-        foreach($wus as $wu){
-            $x = "<in>".$wu->xml_doc."</in>";
-            $x = simplexml_load_string($x);
-            global $fanout;
-            foreach($x->workunit->file_ref as $fr){
-                $pname = (string)$fr->file_name;
-                $ufiles[] = $pname;
-            }
-        }
-    }
-    $dir = sandbox_dir($user);
-    $path = $dir."/".$file;
-    list($err, $size, $md5) = sandbox_parse_link_file($path);
-    if (!$err){
-        $f = sandbox_file_name($user, $md5);
-        foreach($ufiles as $uf) {
-            if (strcmp($f,$uf) == 0){
-                return true;
-            }
-        }
-    }
-    return false;
+function copy_sandbox_file($user, $fname, $dir) {
+    $sbdir = sandbox_dir($user);
+    copy("$sbdir/$fname", "$dir/$fname");
+    copy("$sbdir/.md5/$fname", "$dir/.md5/$fname");
 }
 
 ?>
diff --git a/html/inc/submit_util.inc b/html/inc/submit_util.inc
index f53ad458e7..bce125d5c3 100644
--- a/html/inc/submit_util.inc
+++ b/html/inc/submit_util.inc
@@ -288,4 +288,40 @@ function boinc_get_wu_output_files_url($user, $wu_id) {
     return "get_output.php?cmd=workunit_files&wu_id=$wu_id&auth_str=$auth_str";
 }
 
+////////////////// FILE INFO FILES //////////////
+
+// these are used:
+// 1) in user file sandbox
+// 2) in BUDA app variant dirs
+// in each case a file dir/foo has an info file dir/.md5/foo
+// containing its md5 and size
+// (same format as .md5 files in download hierarchy)
+
+// get the MD5 and size of a file
+//
+function get_file_info($path) {
+    $md5 = md5_file($path);
+    $s = stat($path);
+    $size = $s['size'];
+    return [$md5, $size];
+}
+
+// write a "info file" containing MD5 and size
+//
+function write_info_file($path, $md5, $size) {
+    file_put_contents($path, "$md5 $size");
+}
+
+// parse info file and return [md5, size]
+//
+function parse_info_file($path) {
+    if (!file_exists($path)) return null;
+    $x = file_get_contents($path);
+    $n = sscanf($x, "%s %d", $md5, $size);
+    if ($n != 2 || strlen($md5)!=32) {
+        return null;
+    }
+    return [$md5, $size];
+}
+
 ?>
diff --git a/html/inc/util.inc b/html/inc/util.inc
index 31c3460e9a..195bc9b84d 100644
--- a/html/inc/util.inc
+++ b/html/inc/util.inc
@@ -1133,10 +1133,8 @@ function credit_to_gflop_hours($c) {
     return $c/(200/24);
 }
 
-function do_download($path,$name="") {
-    if (strcmp($name,"") == 0) {
-        $name=basename($path);
-    }
+function do_download($path) {
+    $name=basename($path);
     header('Content-Description: File Transfer');
     header('Content-Type: application/octet-stream');
     header('Content-Disposition: attachment; filename='.$name);
diff --git a/html/user/buda.php b/html/user/buda.php
new file mode 100644
index 0000000000..46d3d8ec5a
--- /dev/null
+++ b/html/user/buda.php
@@ -0,0 +1,330 @@
+<?php
+// This file is part of BOINC.
+// https://boinc.berkeley.edu
+// Copyright (C) 2024 University of California
+//
+// BOINC is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation,
+// either version 3 of the License, or (at your option) any later version.
+//
+// BOINC is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with BOINC.  If not, see <http://www.gnu.org/licenses/>.
+
+// web interface for managing BUDA science apps
+//
+// in the following, 'app' means BUDA science app
+// and 'variant' means a variant of one of these
+//
+// files can have 3 names
+// - sandbox name
+// - physical name (e.g. sb_<md5>)
+// - logical name (how the science app refers to it)
+
+require_once('../inc/util.inc');
+require_once('../inc/sandbox.inc');
+require_once('../inc/submit_util.inc');
+
+display_errors();
+
+$buda_root = "../../buda_apps";
+
+// show list of BUDA apps and variants,
+// w/ buttons for adding and deleting
+//
+function app_list($notice=null) {
+    global $buda_root;
+    if (!is_dir($buda_root)) {
+        mkdir($buda_root);
+    }
+    page_head('Docker apps');
+    if ($notice) {
+        echo "$notice <p>\n";
+    }
+    $dirs = scandir($buda_root);
+    foreach ($dirs as $dir) {
+        if ($dir[0] == '.') continue;
+        show_app($dir);
+    }
+    echo '<hr>';
+    show_button_small('buda.php?action=app_form', 'Add app');
+    page_tail();
+}
+
+function show_app($dir) {
+    global $buda_root;
+    $indent = "&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp";
+    echo "<hr><font size=+3>$dir</font>\n";
+    echo "<p>$indent Variants (click for details):<ul>";
+    $pcs = scandir("$buda_root/$dir");
+    foreach ($pcs as $pc) {
+        if ($pc[0] == '.') continue;
+        echo "<li><a href=buda.php?action=variant_view&app=$dir&variant=$pc>$pc</href>";
+        show_button_small("buda.php?action=variant_delete&app=$dir&variant=$pc", 'Delete variant');
+        show_button_small(
+            "buda_submit.php?app=$dir&variant=$pc", "Submit jobs"
+        );
+    }
+    echo '</ul>';
+    echo $indent;
+    show_button_small("buda.php?action=variant_form&app=$dir", 'Add variant');
+    echo "<p>";
+    echo "<p>";
+    show_button_small(
+        "buda.php?action=app_delete&app=$dir", "Delete app '$dir'"
+    );
+}
+
+function variant_view() {
+    global $buda_root;
+    $app = get_str('app');
+    $variant = get_str('variant');
+    page_head("App $app variant $variant");
+    $dir = "$buda_root/$app/$variant";
+    start_table();
+    table_header('name', 'size', 'md5');
+    foreach(scandir($dir) as $f) {
+        if ($f[0] == '.') continue;
+        [$size, $md5] = parse_info_file("$dir/.md5/$f");
+        table_row(
+            "<a href=buda.php?action=view_file&app=$app&variant=$variant&fname=$f>$f</a>",
+            $size,
+            $md5
+        );
+    }
+    end_table();
+    page_tail();
+}
+
+// form for creating app variant.
+// Currently doesn't support indirect files.
+// doing this would require checkboxes for indirect
+//
+// Could have other stuff like
+//      - min_quorum, max_total_results
+//      - rsc_disk_bound, rsc_memory_bound
+// or does this belong in job submission?
+//
+function variant_form($user) {
+    $sbitems = sandbox_select_items($user);
+    $app = get_str('app');
+
+    page_head("Create variant of Docker app $app");
+    form_start('buda.php');
+    form_input_hidden('app', $app);
+    form_input_hidden('action', 'variant_action');
+    form_input_text('Plan class', 'plan_class');
+    form_select('Dockerfile', 'dockerfile', $sbitems);
+    form_select('Main program', 'main_prog', $sbitems);
+    form_select_multiple('Other application files', 'others', $sbitems);
+    form_input_text('Input file names', 'input_file_names');
+    form_input_text('Output file names', 'output_file_names');
+    form_submit('OK');
+    form_end();
+    page_tail();
+}
+
+// copy file from sandbox to variant dir, and stage to download hier
+//
+function copy_and_stage_file($user, $fname, $dir, $variant) {
+    copy_sandbox_file($user, $fname, $dir);
+    [$md5, $size] = parse_info_file("$dir/.md5/$fname");
+    $phys_name = sprintf('buda_%s_%s_%s', $app, $variant, $md5);
+    stage_file_aux("$dir/$fname", $md5, $size, $phys_name);
+}
+
+// create variant
+//
+function variant_action($user) {
+    global $buda_root;
+    $plan_class = get_str('plan_class');
+    $app = get_str('app');
+    $dockerfile = get_str('dockerfile');
+    $main_prog = get_str('main_prog');
+    $others = get_array('others');
+    $input_file_names = explode(' ', get_str('input_file_names'));
+    $output_file_names = explode(' ', get_str('output_file_names'));
+
+    if (file_exists("$buda_root/$app/$plan_class")) {
+        error_page("Variant '$plan_class' already exists.");
+    }
+    $dir = "$buda_root/$app/$plan_class";
+    mkdir($dir);
+    mkdir("$dir/.md5");
+
+    // copy files from sandbox to variant dir
+    //
+    copy_and_stage_file($user, $dockerfile, $dir, $app, $variant);
+    copy_and_stage_file($user, $main_prog, $dir, $app, $variant);
+    foreach ($others as $fname) {
+        copy_and_stage_file($user, $fname, $dir, $app, $variant);
+    }
+
+    // create input template
+    //
+    $x = "<input_template>\n";
+    $ninfiles = 2 + count($input_file_names) + count($others);
+    for ($i=0; $i<$ninfiles; $i++) {
+        $x .= "   <file_info>\n   </file_info>\n";
+    }
+    $x .= "   <workunit>\n";
+    $x .= file_ref_in('Dockerfile');
+    $x .= file_ref_in($main_prog);
+    foreach ($others as $fname) {
+        $x .= file_ref_in($fname);
+    }
+    foreach ($input_file_names as $fname) {
+        $x .= file_ref_in($fname);
+    }
+    $x .= "   </workunit>\n<input_template>\n";
+    file_put_contents("$dir/template_in", $x);
+
+    // create output template
+    //
+    $x = "<output_template>\n";
+    $i = 0;
+    foreach ($output_file_names as $fname) {
+        $x .= file_info_out($i++);
+    }
+    $x .= "   <result>\n";
+    $i = 0;
+    foreach ($output_file_names as $fname) {
+        $x .= file_ref_out($i++, $fname);
+    }
+    $x .= "   </result>\n</output_template>\n";
+    file_put_contents("$dir/template_out", $x);
+
+    // Note: we don't currently allow indirect file access.
+    // If we did, we'd need to create job.toml to mount project dir
+
+    app_list("Variant $plan_class added for app $app.");
+}
+
+function file_ref_in($fname) {
+    return(sprintf(
+'      <file_ref>
+          <open_name>%s</open_name>
+       </file_ref>
+',
+        $fname
+    ));
+}
+function file_info_out($i) {
+    return sprintf(
+'    <file_info>
+        <name><OUTFILE_%d/></name>
+        <generated_locally/>
+        <upload_when_present/>
+        <max_nbytes>5000000</max_nbytes>
+        <url><UPLOAD_URL/></url>
+    </file_info>
+',
+        $i
+    );
+}
+
+function file_ref_out($i, $fname) {
+    return sprintf(
+'        <file_ref>
+            <file_name><OUTFILE_%d/></file_name>
+            <open_name>%s</open_name>
+        </file_ref>
+',      $i, $fname
+    );
+}
+
+function variant_delete() {
+    global $buda_root;
+    $app = get_str('app');
+    $variant = get_str('variant');
+    $confirmed = get_str('confirmed', true);
+    if ($confirmed) {
+        $dir = "$buda_root/$app/$variant";
+        // delete staged files
+        //
+        foreach (scandir("$dir/.md5") as $fname) {
+            if ($fname[0] == '.') continue;
+            [$size, $md5] = parse_file_info("$dir/$fname");
+            $phys_name = buda_app_file_phys_name($app, $variant, $md5);
+            $phys_path = download_path($phys_name);
+            unlink($phys_path);
+        }
+        system("rm -r $buda_root/$app/$variant", $ret);
+        if ($ret) {
+            error_page("delete failed");
+        }
+        $notice = "Variant $variant of app $app removed.";
+        app_list($notice);
+    } else {
+        page_head("Confirm");
+        echo "Are you sure want to delete variant $variant of app $app?
+            <p>
+        ";
+        show_button(
+            "buda.php?action=variant_delete&app=$app&variant=$variant&confirmed=yes",
+            "Yes"
+        );
+        page_tail();
+    }
+}
+
+function app_form() {
+    page_head("Create Docker app");
+    form_start();
+    form_input_text('Name', 'name');
+    form_submit('OK');
+    form_end();
+    page_tail();
+}
+
+function app_action() {
+    global $buda_root;
+    $name = get_str('name');
+    $dir = "$buda_root/$name";
+    if (file_exists($dir)) {
+        error_page("App $name already exists.");
+    }
+    mkdir($dir);
+    header("Location: buda.php");
+}
+
+function view_file() {
+    global $buda_root;
+    $app = get_str('app');
+    $variant = get_str('variant');
+    $fname = get_str('fname');
+    echo "<pre>\n";
+    readfile("$buda_root/$app/$variant/$fname");
+}
+
+$user = get_logged_in_user();
+$action = get_str('action', true);
+switch ($action) {
+case 'app_form':
+    app_form(); break;
+case 'app_action':
+    app_action(); break;
+case 'app_delete':
+    app_delete(); break;
+case 'variant_view':
+    variant_view($user); break;
+case 'variant_form':
+    variant_form($user); break;
+case 'variant_action':
+    variant_action($user); break;
+case 'variant_delete':
+    variant_delete(); break;
+case 'view_file':
+    view_file(); break;
+case null:
+    app_list(); break;
+default:
+    error_page("unknown action $action");
+}
+
+?>
diff --git a/html/user/buda_submit.php b/html/user/buda_submit.php
new file mode 100644
index 0000000000..0dc2379a86
--- /dev/null
+++ b/html/user/buda_submit.php
@@ -0,0 +1,73 @@
+<?php
+// This file is part of BOINC.
+// https://boinc.berkeley.edu
+// Copyright (C) 2024 University of California
+//
+// BOINC is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation,
+// either version 3 of the License, or (at your option) any later version.
+//
+// BOINC is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with BOINC.  If not, see <http://www.gnu.org/licenses/>.
+
+// web interface for submitting BUDA jobs
+
+require_once('../inc/util.inc');
+require_once('../inc/sandbox.inc');
+
+display_errors();
+
+function submit_form($user) {
+    $sbitems_zip = sandbox_select_items($user, '/.zip$/');
+    if (!$sbitems_zip) {
+        error_page("No .zip files in your sandbox.");
+    }
+    $app = get_str('app');
+    $variant = get_str('variant');
+
+    page_head("Submit jobs to $app ($variant)");
+    form_start('buda_submit.php');
+    form_input_hidden('action', 'submit');
+    form_input_hidden('app', $app);
+    form_input_hidden('variant', $variant);
+    form_input_text('Batch name', 'batch_name');
+    form_select('Job file', 'job_file', $sbitems_zip);
+    form_submit('OK');
+    form_end();
+    page_tail();
+}
+
+function handle_submit() {
+    // stage app files if not already staged
+    //
+
+    // create batch
+    //
+
+    // unzip batch file
+    //
+
+    // stage top-level input files
+    //
+
+    // scan jobs; stage per-job input files and make create_work input
+    //
+
+    // create jobs
+}
+
+$user = get_logged_in_user();
+$action = get_str('action', true);
+if ($action == 'submit') {
+    handle_submit();
+} else {
+    submit_form($user);
+}
+
+?>
diff --git a/html/user/sandbox.php b/html/user/sandbox.php
index 1aecbda361..293606968c 100644
--- a/html/user/sandbox.php
+++ b/html/user/sandbox.php
@@ -16,14 +16,10 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with BOINC.  If not, see <http://www.gnu.org/licenses/>.
 
-// Per-user "file sandboxes" for job submission.
-// These are stored in project-root/sandbox/USERID/
-//
-// The entries in a sandbox directory have contents
-// size md5
-//
-// The actual files are stored in the download hierarchy,
-// with sb_userid_MD5 as the physical name
+// Per-user "file sandboxes".
+// Files are stored in <project>/sandbox/<userid>/
+// File infos (md5/size) are scored in a parallel dir
+// <project>/sandbox/<userid>/.md5/
 
 // NOTE: PHP's default max file upload size is 2MB.
 // To increase this, edit /etc/php.ini, and change, e.g.
@@ -32,33 +28,31 @@
 // post_max_size = 64M
 
 require_once("../inc/sandbox.inc");
-require_once("../inc/submit_db.inc");
 require_once("../inc/submit_util.inc");
 
 display_errors();
 
 function list_files($user, $notice) {
     $dir = sandbox_dir($user);
-    $d = opendir($dir);
-    if (!$d) error_page("Can't open sandbox directory");
+    if (!is_dir($dir)) error_page("Can't open sandbox directory");
     page_head("File sandbox");
     if ($notice) {
         echo "<p>$notice<hr>";
     }
     echo "
         <p>
+        <h3>Upload files</h3>
         <form action=sandbox.php method=post ENCTYPE=\"multipart/form-data\">
         <input type=hidden name=action value=upload_file>
-        Upload files to your sandbox:
         <p><p><input size=80 type=file name=\"new_file[]\" multiple=\"multiple\">
         <p> <input class=\"btn btn-success\" type=submit value=Upload>
         </form>
         <hr>
+        <h3>Sandbox contents</h3>
     ";
     $files = array();
-    while (($f = readdir($d)) !== false) {
-        if ($f == '.') continue;
-        if ($f == '..') continue;
+    foreach (scandir($dir) as $f) {
+        if ($f[0] == '.') continue;
         $files[] = $f;
     }
     if (count($files) == 0) {
@@ -66,19 +60,10 @@ function list_files($user, $notice) {
     } else {
         sort($files);
         start_table();
-        table_header("Name<br><p class=\"text-muted\">(click to view)</p>", "Modified", "Size (bytes)", "MD5", "Delete","Download");
+        table_header("Name<br><p class=\"text-muted\">(click to view text files)</p>", "Modified", "Size (bytes)", "MD5", "Delete","Download");
         foreach ($files as $f) {
+            [$md5, $size] = sandbox_parse_info_file($user, $f);
             $path = "$dir/$f";
-            list($error, $size, $md5) = sandbox_parse_link_file($path);
-            if ($error) {
-                table_row($f, "Can't parse link file", "", "<a href=sandbox.php?action=delete_files&name=$f>delete</a>");
-                continue;
-            }
-            $p = sandbox_physical_path($user, $md5);
-            if (!is_file($p)) {
-                table_row($f, "Physical file not found", "", "");
-                continue;
-            }
             $ct = time_str(filemtime($path));
             table_row(
                 "<a href=sandbox.php?action=view_file&name=$f>$f</a>",
@@ -100,10 +85,13 @@ function list_files($user, $notice) {
     page_tail();
 }
 
+// upload one or more files
+
 function upload_file($user) {
     $notice = "";
+    $dir = sandbox_dir($user);
     $count = count($_FILES['new_file']['tmp_name']);
-    for ($i = 0; $i < $count; $i++) {
+    for ($i=0; $i<$count; $i++) {
         $tmp_name = $_FILES['new_file']['tmp_name'][$i];
         if (!is_uploaded_file($tmp_name)) {
             error_page("$tmp_name is not uploaded file");
@@ -112,79 +100,48 @@ function upload_file($user) {
         if (strstr($name, "/")) {
             error_page("no / allowed");
         }
-        $md5 = md5_file($tmp_name);
-        $s = stat($tmp_name);
-        $size = $s['size'];
-        [$exists, $elf] = sandbox_lf_exists($user, $md5);
-        if (!$exists){
-            // move file to download dir
-            //
-            $phys_path = sandbox_physical_path($user, $md5);
-            move_uploaded_file($tmp_name, $phys_path);
+        if (file_exists("$dir/$name")) {
+            $notice .= "can't upload $name; file exists.<br>";
+            continue;
         }
+        move_uploaded_file($tmp_name, "$dir/$name");
 
-        // write link file
+        // write info file
         //
-        $dir = sandbox_dir($user);
-        $link_path = "$dir/$name";
-        sandbox_write_link_file($link_path, $size, $md5);
+        [$md5, $size] = get_file_info("$dir/$name");
+        write_info_file("$dir/.md5/$name", $md5, $size);
+
         $notice .= "Uploaded file <strong>$name</strong><br/>";
     }
     list_files($user, $notice);
 }
 
-// delete a link to a file.
-// check if currently being used by a batch.
-// If the last link w/ that contents, delete the file itself
+// delete a sandbox file.
 //
 function delete_file($user) {
     $name = get_str('name');
     $dir = sandbox_dir($user);
-    list($error, $size, $md5) = sandbox_parse_link_file("$dir/$name");
-    if ($error) {
-        error_page("can't parse link file");
-    }
-    $p = sandbox_physical_path($user, $md5);
-    if (!is_file($p)) {
-        error_page("physical file is missing");
-    }
-    $bused = sandbox_file_in_use($user, $name);
-    if ($bused){
-        $notice = "<strong>$name</strong> is being used by batch(es), you can not delete it now!<br/>";
-    } else{
-        unlink("$dir/$name");
-        $notice = "<strong>$name</strong> was deleted from your sandbox<br/>";
-        [$exists, $elf] = sandbox_lf_exists($user, $md5);
-        if (!$exists) {
-            unlink($p);
-        }
-
-    }
+    unlink("$dir/$name");
+    unlink("$dir/.md5/$name");
+    $notice = "<strong>$name</strong> was deleted from your sandbox<br/>";
     list_files($user, $notice);
-    //Header("Location: sandbox.php");
 }
+
 function download_file($user) {
     $name = get_str('name');
     $dir = sandbox_dir($user);
-    list($err, $size, $md5) = sandbox_parse_link_file("$dir/$name");
-    if ($err) {
-        error_page("can't parse link file");
-    }
-    $p = sandbox_physical_path($user, $md5);
-    if (!is_file($p)) {
-        error_page("$p does not exist!");
-    }
-    do_download($p, $name);
+    do_download("$dir/$name");
 }
+
 function view_file($user) {
     $name = get_str('name');
     $dir = sandbox_dir($user);
-    list($error, $size, $md5) = sandbox_parse_link_file("$dir/$name");
-    if ($error) error_page("no such link file");
-    $p = sandbox_physical_path($user, $md5);
-    if (!is_file($p)) error_page("no such physical file");
+    $path = "$dir/$name";
+    if (!is_file($path)) {
+        error_path("no such file $name");
+    }
     echo "<pre>\n";
-    readfile($p);
+    readfile($path);
     echo "</pre>\n";
 }
 
diff --git a/tools/submit_buda b/tools/submit_buda
index 5b5950c3a7..add5f0abfb 100755
--- a/tools/submit_buda
+++ b/tools/submit_buda
@@ -1,35 +1,40 @@
 #! /usr/bin/env php
 <?php
 
-// submit a job for the Docker universal app (which must be named 'buda')
+// submit a job for a BUDA (BOINC Universal Docker app) science app
 //
-// submit_buda [--buda_dir dir] [--verbose] infile ...
+// submit_buda [options] sci_app infile ...
 //
-// the buda dir (default buda_dir/) must contain
-// - buda_in, buda_out: input, output templates
-// - other files; typically
-//      a Dockerfile
-//      job.toml
-//      main.sh script
-//      science executable
-// - file_list
-//      a list of the other filenames (one per line)
-//      in the order of the input template
+// --buda_root dir      root of BUDA app hierarchy, default 'buda_apps'
+// --variant x          variant, default 'cpu'
+// --verbose
 
-$buda_dir = 'buda_dir';
+$buda_root = 'buda_apps';
 $infiles = [];
 $verbose = false;
+$variant = 'cpu';
+$sci_app = null;
 
 for ($i=1; $i<$argc; $i++) {
-    if ($argv[$i] == '--buda_dir') {
-        $buda_dir = $argv[++$i];
+    if ($argv[$i] == '--buda_root') {
+        $buda_root = $argv[++$i];
+    } else if ($argv[$i] == '--variant') {
+        $variant = $argv[++$i];
     } else if ($argv[$i] == '--verbose') {
         $verbose = true;
     } else {
-        $infiles[] = $argv[$i];
+        if (!$sci_app) {
+            $sci_app = $argv[$i];
+        } else {
+            $infiles[] = $argv[$i];
+        }
     }
 }
 
+$buda_dir = "$buda_root/$sci_app/$variant";
+if (!is_dir($buda_dir)) {
+    die("No version dir $buda_dir\n");
+}
 if (!file_exists("$buda_dir/template_in")) {
     die("no input template\n");
 }