diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 9459628c..b1d29e70 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -28,9 +28,7 @@ jobs:
 
       - name: Run tests
         run: |
-          cd ..
-          cp -r try ~
-          cd ~/try
+          sudo ./setup.sh
           scripts/run_tests.sh
 
       - name: Upload script
diff --git a/Vagrantfile b/Vagrantfile
index 5972795a..1b3f766a 100644
--- a/Vagrantfile
+++ b/Vagrantfile
@@ -11,9 +11,10 @@ Vagrant.configure("2") do |config|
     debian.vm.provision "file", source: "./", destination: "/home/vagrant/try"
     debian.vm.provision "shell", privileged: false, inline: "
       sudo apt-get update
-      sudo apt-get install -y git expect curl
+      sudo apt-get install -y git expect curl libcap2-bin
       sudo chown -R vagrant:vagrant try
       cd try
+      sudo ./setup.sh
       scripts/run_tests.sh
     "
   end
@@ -24,9 +25,10 @@ Vagrant.configure("2") do |config|
     debianrustup.vm.provision "file", source: "./", destination: "/home/vagrant/try"
     debianrustup.vm.provision "shell", privileged: false, inline: "
       sudo apt-get update
-      sudo apt-get install -y curl
+      sudo apt-get install -y curl libcap2-bin
       sudo chown -R vagrant:vagrant try
       cd try
+      sudo ./setup.sh
       mkdir rustup
       ./try -D rustup \"curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y\"
       ls -lah rustup/upperdir/home/vagrant/.cargo/bin
@@ -39,7 +41,7 @@ Vagrant.configure("2") do |config|
     debianlvm.vm.provision "file", source: "./", destination: "/home/vagrant/try"
     debianlvm.vm.provision "shell", privileged: false, inline: "
       sudo apt-get update
-      sudo apt-get install -y git expect lvm2 mergerfs curl
+      sudo apt-get install -y git expect lvm2 mergerfs curl libcap2-bin
 
       # Create an image for the lvm disk
       sudo fallocate -l 2G /root/lvm_disk.img
@@ -65,6 +67,7 @@ Vagrant.configure("2") do |config|
       sudo chown -R vagrant:vagrant /mnt/lv0/try
 
       cd /mnt/lv0/try
+      sudo ./setup.sh
       scripts/run_tests.sh
     "
   end
@@ -77,6 +80,7 @@ Vagrant.configure("2") do |config|
       sudo yum install -y git expect curl
       sudo chown -R vagrant:vagrant try
       cd try
+      sudo ./setup.sh
       TRY_TOP=$(pwd) scripts/run_tests.sh
     "
   end
@@ -89,6 +93,7 @@ Vagrant.configure("2") do |config|
       sudo yum install -y git expect curl
       sudo chown -R vagrant:vagrant try
       cd try
+      sudo ./setup.sh
       TRY_TOP=$(pwd) scripts/run_tests.sh
     "
   end
diff --git a/setup.sh b/setup.sh
new file mode 100755
index 00000000..679a3e9c
--- /dev/null
+++ b/setup.sh
@@ -0,0 +1,5 @@
+#!/bin/sh
+
+wget https://github.com/ezrizhu/gidmapper/releases/download/0.0.3/gidmapper -O /usr/bin/gidmapper
+chmod +x /usr/bin/gidmapper
+setcap 'CAP_SETGID=ep' /usr/bin/gidmapper
diff --git a/test/fileowner.sh b/test/fileowner.sh
new file mode 100755
index 00000000..8ecb4eb4
--- /dev/null
+++ b/test/fileowner.sh
@@ -0,0 +1,39 @@
+#!/bin/sh
+
+TRY_TOP="${TRY_TOP:-$(git rev-parse --show-toplevel --show-superproject-working-tree)}"
+TRY="$TRY_TOP/try"
+
+cleanup() {
+    cd /
+
+    if [ -d "$try_workspace" ]
+    then
+        rm -rf "$try_workspace" >/dev/null 2>&1
+    fi
+
+    if [ -f "$expected" ]
+    then
+        rm "$expected"
+    fi
+
+    if [ -f "$target" ]
+    then
+        rm "$target"
+    fi
+}
+
+trap 'cleanup' EXIT
+
+try_workspace="$(mktemp -d)"
+cd "$try_workspace" || return 9
+touch test
+
+# Set up expected output
+expected="$(mktemp)"
+ls -l >"$expected"
+
+# Set up target output
+target="$(mktemp)"
+
+sudo "$TRY" ls -l | tee "$target" || return 1
+diff -q "$expected" "$target"
diff --git a/test/gidmapping.sh b/test/gidmapping.sh
new file mode 100755
index 00000000..b9c5e331
--- /dev/null
+++ b/test/gidmapping.sh
@@ -0,0 +1,14 @@
+#!/bin/sh
+
+TRY_TOP="${TRY_TOP:-$(git rev-parse --show-toplevel --show-superproject-working-tree)}"
+TRY="$TRY_TOP/try"
+
+control=$(id -Gn)
+testing=$("$TRY" -D "$(mktemp -d)" id -Gn 2>/dev/null)
+
+if [ "$control" = "$testing" ]
+then
+    exit 0
+else
+    exit 1
+fi
diff --git a/test/toplevel-perms.sh b/test/toplevel-perms.sh
index 9f654a8a..71584aed 100755
--- a/test/toplevel-perms.sh
+++ b/test/toplevel-perms.sh
@@ -34,9 +34,7 @@ cd "$try_workspace" || return 9
 touch test
 
 cmd="$(mktemp)"
-echo "find / -maxdepth 1 -print0 | xargs -0 ls -ld | awk '{print substr(\$1, 1, 10), \$9, \$10, \$11}' | grep -v 'proc' | grep -v 'swap'" > "$cmd"
-# Use this after gidmapper to show user and group ownership
-#echo "find / -maxdepth 1 -print0 | xargs -0 ls -ld | awk '{print substr(\$1, 1, 10), \$3, \$4, \$9, \$10, \$11}' | grep -v 'proc' | grep -v 'swap'" > "$cmd"
+echo "find / -maxdepth 1 -type d -print0 | xargs -0 ls -ld | awk '{print substr(\$1, 1, 10), \$9, \$10, \$11}' | grep -v '/proc' " > "$cmd"
 
 # Set up expected output
 expected="$(mktemp)"
@@ -45,6 +43,6 @@ sh "$cmd" >"$expected"
 # Set up target output
 target="$(mktemp)"
 
-"$TRY" "sh $cmd" > "$target" || return 1
-#diff -q "$expected" "$target"
+# shellcheck disable=SC2024 # sudo won't be used in > $target redirection
+sudo "$TRY" "sh $cmd" > "$target" || return 1
 diff "$expected" "$target"
diff --git a/test/uidmapping.sh b/test/uidmapping.sh
new file mode 100755
index 00000000..93758b01
--- /dev/null
+++ b/test/uidmapping.sh
@@ -0,0 +1,14 @@
+#!/bin/sh
+
+TRY_TOP="${TRY_TOP:-$(git rev-parse --show-toplevel --show-superproject-working-tree)}"
+TRY="$TRY_TOP/try"
+
+control=$(id -un)
+testing=$(sudo "$TRY" -D "$(mktemp -d)" -u "$USER" id -un)
+
+if [ "$control" = "$testing" ]
+then
+    exit 0
+else
+    exit 1
+fi
diff --git a/try b/try
index dc948f15..a8803dba 100755
--- a/try
+++ b/try
@@ -172,6 +172,12 @@ autodetect_union_helper() {
     fi
 }
 
+# notify the mapper that we're up
+echo "a" > "$SOCKET"
+
+# wait for mapper to finish
+cat "$SOCKET" > /dev/null
+
 # Detect if union_helper is set, if not, we try to autodetect them
 if [ -z "$UNION_HELPER" ]
 then
@@ -257,12 +263,17 @@ EOF
     cat >"$chroot_executable" <<EOF
 #!/bin/sh
 
-unset START_DIR SANDBOX_DIR UNION_HELPER DIRS_AND_MOUNTS TRY_EXIT_STATUS
+unset START_DIR SANDBOX_DIR UNION_HELPER DIRS_AND_MOUNTS TRY_EXIT_STATUS SOCKET
 unset script_to_execute chroot_executable try_mount_log
 
 mount -t proc proc /proc &&
-cd "$START_DIR" &&
-. "$script_to_execute"
+if [ "$EUSER" ]
+then
+    su - $EUSER -c "cd "$START_DIR" && sh $script_to_execute"
+else
+    cd "$START_DIR" &&
+    . "$script_to_execute"
+fi
 EOF
 
     echo "$@" >"$script_to_execute"
@@ -270,17 +281,28 @@ EOF
     # `$script_to_execute` need not be +x to be sourced
     chmod +x "$mount_and_execute" "$chroot_executable"
 
+    if [ "$EUSER" ]
+    then
+        chown "$EUSER" "$script_to_execute"
+    fi
+
     # enable job control so interactive commands will play nicely with try asking for user input later(for committing). #5
     [ -t 0 ] && set -m
 
+    SOCKET="$(mktemp -u)"
+    mkfifo "$SOCKET"
+    export SOCKET
+
+    # Running mapper in a subshell to suppress job control [1] + Done message
+    (mapper&)
+
     # --mount: mounting and unmounting filesystems will not affect the rest of the system outside the unshare
-    # --map-root-user: map to the superuser UID and GID in the newly created user namespace.
     # --user: the process will have a distinct set of UIDs, GIDs and capabilities.
     # --pid: create a new process namespace (needed fr procfs to work right)
     # --fork: necessary if we do --pid
     #         "Creation of a persistent PID namespace will fail if the --fork option is not also specified."
     # shellcheck disable=SC2086 # we want field splitting!
-    unshare --mount --map-root-user --user --pid --fork $EXTRA_NS "$mount_and_execute"
+    unshare --mount --user --pid --fork $EXTRA_NS "$mount_and_execute"
     TRY_EXIT_STATUS=$?
 
     # remove symlink
@@ -533,6 +555,30 @@ error() {
     exit "$exit_status"
 }
 
+################################################################################
+# Change uid/gid mapping
+################################################################################
+
+mapper() {
+    cat "$SOCKET" > /dev/null
+    # Get the pid of the unshare process with current pid as parent
+    pid=$(pgrep -P $$ -f unshare)
+
+    # Map root user to current user, and all groups
+    # Usage: gidmapper targetpid outeruid inneruid uidcount outergid innergid uidcount
+    if [ "$(id -u)" = 0 ]
+    then
+        # If we're running as root, we can map all the users
+        gidmapper "$pid" 0 0 65535 0 0 65535
+    else
+        # If not running as root, we can only mount the caller user
+        gidmapper "$pid" 0 "$(id -u)" 1 0 0 65535
+    fi
+
+    # Notify the unshare process that we have finished
+    echo "a" > "$SOCKET"
+}
+
 ################################################################################
 # Argument parsing
 ################################################################################
@@ -544,6 +590,7 @@ Usage: $TRY_COMMAND [-nvhyx] [-i PATTERN] [-D DIR] [-U PATH] [-L dir1:dir2:...]
   -n                don't commit or prompt for commit (overrides -y)
   -y                assume yes to all prompts (overrides -n)
   -x                prevent network access (by unsharing the network namespace)
+  -u username       user to run the command with (requires root)
   -i PATTERN        ignore paths that match PATTERN on summary and commit
   -D DIR            work in DIR (implies -n)
   -U PATH           path to unionfs helper (e.g., mergerfs, unionfs-fuse)
@@ -571,13 +618,19 @@ NO_COMMIT="interactive"
 # Includes all patterns given using the `-i` flag; will be used with `grep -f`
 IGNORE_FILE="$(mktemp)"
 
-while getopts ":yvnhxi:D:U:L:" opt
+while getopts ":yvnhxu:i:D:U:L:" opt
 
 do
     case "$opt" in
         (y)   NO_COMMIT="commit";;
         (n)   NO_COMMIT="show";;
         (i)   echo "$OPTARG" >>"$IGNORE_FILE";;
+        (u)   if [ "$(id -u)" -ne "0" ]
+              then
+                  error "need root for -u" 2
+              fi
+              EUSER="$OPTARG"
+              export EUSER;;
         (D)   if ! [ -d "$OPTARG" ]
               then
                   error "could not find sandbox directory '$OPTARG'" 2
diff --git a/util/mapper/mapper.c b/util/mapper/mapper.c
new file mode 100644
index 00000000..4e94502e
--- /dev/null
+++ b/util/mapper/mapper.c
@@ -0,0 +1,56 @@
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+void* map_uids(void* args) {
+  char *targetpid = argv[1];
+  char *outeruid = argv[2];
+  char *inneruid = argv[3];
+  char *uidcount = argv[4];
+  char *outergid = argv[5];
+  char *innergid = argv[6];
+  char *gidcount = argv[7];
+
+  // Build path strings
+  char uid_path[100];
+  sprintf(uid_path, "/proc/%s/uid_map", targetpid);
+
+  char gid_path[100];
+  sprintf(gid_path, "/proc/%s/gid_map", targetpid);
+
+  // Build mapping strings
+  char uid_map[100];
+  sprintf(uid_map, "%s %s %s", outeruid, inneruid, uidcount);
+
+  char gid_map[100];
+  sprintf(gid_map, "%s %s %s", outergid, innergid, gidcount);
+
+  // Write mappings
+  FILE *uid_file = fopen(uid_path, "w");
+  fprintf(uid_file, "%s", uid_map);
+  fclose(uid_file);
+
+  FILE *gid_file = fopen(gid_path, "w");
+  fprintf(gid_file, "%s", gid_map);
+  fclose(gid_file);
+
+  return 0;
+}
+
+int main(int argc, char* argv[]) {
+
+  char *usage = "Usage: gidmapper targetpid outeruid inneruid uidcount outergid innergid gidcount";
+
+  if(argc < 8) {
+    fprintf(stderr, "%s\n", usage);
+    exit(1);
+  }
+
+  pthread_t mapper_thread;
+  pthread_create(&mapper_thread, NULL, map_uids, NULL);
+
+  pthread_join(mapper_thread, NULL);
+
+  return 0;
+}