Here is console for successful run rootless on Ubuntu 18.  So why not working on CentOS 7.x?

=====

Script started on 2019-10-14 11:55:21-0400

]0;eae@f12n13: /home/eae eae@f12n13:~$ podman info
host:
  BuildahVersion: 1.9.0
  Conmon:
    package: 'conmon: /usr/libexec/podman/conmon'
    path: /usr/libexec/podman/conmon
    version: 'conmon version 1.0.0-rc2, commit: unknown'
  Distribution:
    distribution: ubuntu
    version: "18.04"
  MemFree: 284860088320
  MemTotal: 548435001344
  OCIRuntime:
    package: 'cri-o-runc: /usr/lib/cri-o-runc/sbin/runc'
    path: /usr/lib/cri-o-runc/sbin/runc
    version: 'runc version spec: 1.0.1-dev'
  SwapFree: 23127326720
  SwapTotal: 23152492544
  arch: ppc64le
  cpus: 192
  hostname: f12n13
  kernel: 4.15.0-55-generic
  os: linux
  rootless: true
  uptime: 979h 10m 16.18s (Approximately 40.79 days)
registries:
  blocked: null
  insecure: null
  search:
  - docker.io
store:
  ConfigFile: /home/eae/.config/containers/storage.conf
  ContainerStore:
    number: 0
  GraphDriverName: vfs
  GraphOptions: null
  GraphRoot: /tmp/eae/containers/storage
  GraphStatus: {}
  ImageStore:
    number: 3
  RunRoot: /run/user/2018
  VolumePath: /tmp/eae/containers/storage/volumes


]0;eae@f12n13: /home/eae eae@f12n13:~$ cat ./.config/containers/libpod.conf
volume_path = "/tmp/eae/containers/storage/volumes"
image_default_transport = "docker://"
runtime = "runc"
conmon_path = ["/usr/libexec/podman/conmon", "/usr/local/lib/podman/conmon", "/usr/bin/conmon", "/usr/sbin/conmon", "/usr/local/bin/conmon", "/usr/local/sbin/conmon"]
conmon_env_vars = ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"]
cgroup_manager = "cgroupfs"
init_path = "/usr/libexec/podman/catatonit"
static_dir = "/tmp/eae/containers/storage/libpod"
tmp_dir = "/run/user/2018/libpod/tmp"
max_log_size = -1
no_pivot_root = false
cni_config_dir = "/etc/cni/net.d/"
cni_plugin_dir = ["/usr/libexec/cni", "/usr/lib/cni", "/usr/local/lib/cni", "/opt/cni/bin"]
infra_image = "k8s.gcr.io/pause:3.1"
infra_command = "/pause"
enable_port_reservation = true
label = true
network_cmd_path = ""
num_locks = 2048
events_logger = "journald"
EventsLogFilePath = ""
detach_keys = "ctrl-p,ctrl-q"
hooks_dir = ["/etc/containers/oci/hooks.d"]
[runtimes]
  runc = ["/usr/lib/cri-o-runc/sbin/runc"]

]0;eae@f12n13: /home/eae eae@f12n13:~$ cat /etc/containers/oci/hooks.d/oci-nvidia-hook.json
{
  "version": "1.0.0",
  "hook": {
    "path": "/usr/bin/nvidia-container-runtime-hook",
    "args": ["nvidia-container-runtime-hook", "prestart"]
  },
  "when": {
    "always": true
  },
  "stages": ["prestart"]
}



]0;eae@f12n13: /home/eae eae@f12n13:~$ podman --log-level=debug run --rm ibmcom/tensorflow-ppc64le:1.14.0-gpu nvidia-smi
[36mINFO [0m[0000] running as rootless                          
[37mDEBU [0m[0000] Initializing boltdb state at /tmp/eae/containers/storage/libpod/bolt_state.db
[37mDEBU [0m[0000] Using graph driver vfs                      
[37mDEBU [0m[0000] Using graph root /tmp/eae/containers/storage
[37mDEBU [0m[0000] Using run root /run/user/2018                
[37mDEBU [0m[0000] Using static dir /tmp/eae/containers/storage/libpod
[37mDEBU [0m[0000] Using tmp dir /run/user/2018/libpod/tmp      
[37mDEBU [0m[0000] Using volume path /tmp/eae/containers/storage/volumes
[37mDEBU [0m[0000] Set libpod namespace to ""                  
[37mDEBU [0m[0000] [graphdriver] trying provided driver "vfs"  
[37mDEBU [0m[0000] Initializing event backend journald          
[37mDEBU [0m[0000] parsed reference into "[vfs@/tmp/eae/containers/storage+/run/user/2018]docker.io/ibmcom/tensorflow-ppc64le:1.14.0-gpu"
[37mDEBU [0m[0000] parsed reference into "[vfs@/tmp/eae/containers/storage+/run/user/2018]@09f6383a1fbb35ca5fbccf6f0bd21a5c3d5264b6c0b56597fd47a97c99421727"
[37mDEBU [0m[0000] exporting opaque data as blob "sha256:09f6383a1fbb35ca5fbccf6f0bd21a5c3d5264b6c0b56597fd47a97c99421727"
[37mDEBU [0m[0000] parsed reference into "[vfs@/tmp/eae/containers/storage+/run/user/2018]@09f6383a1fbb35ca5fbccf6f0bd21a5c3d5264b6c0b56597fd47a97c99421727"
[37mDEBU [0m[0000] exporting opaque data as blob "sha256:09f6383a1fbb35ca5fbccf6f0bd21a5c3d5264b6c0b56597fd47a97c99421727"
[37mDEBU [0m[0000] parsed reference into "[vfs@/tmp/eae/containers/storage+/run/user/2018]@09f6383a1fbb35ca5fbccf6f0bd21a5c3d5264b6c0b56597fd47a97c99421727"
[37mDEBU [0m[0000] Got mounts: []                              
[37mDEBU [0m[0000] Got volumes: []                              
[37mDEBU [0m[0000] Using slirp4netns netmode                    
[37mDEBU [0m[0000] created OCI spec and options for new container
[37mDEBU [0m[0000] Allocated lock 0 for container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6
[37mDEBU [0m[0000] parsed reference into "[vfs@/tmp/eae/containers/storage+/run/user/2018]@09f6383a1fbb35ca5fbccf6f0bd21a5c3d5264b6c0b56597fd47a97c99421727"
[37mDEBU [0m[0000] exporting opaque data as blob "sha256:09f6383a1fbb35ca5fbccf6f0bd21a5c3d5264b6c0b56597fd47a97c99421727"
[37mDEBU [0m[0002] created container "427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6"
[37mDEBU [0m[0002] container "427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6" has work directory "/tmp/eae/containers/storage/vfs-containers/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6/userdata"
[37mDEBU [0m[0002] container "427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6" has run directory "/run/user/2018/vfs-containers/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6/userdata"
[37mDEBU [0m[0002] New container created "427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6"
[37mDEBU [0m[0002] container "427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6" has CgroupParent "/libpod_parent/libpod-427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6"
[37mDEBU [0m[0002] Not attaching to stdin                      
[37mDEBU [0m[0002] mounted container "427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6" at "/tmp/eae/containers/storage/vfs/dir/6493d899b4a3aa9facb67ec96a1ba381c135c5003b384ac6da1af433d816714f"
[37mDEBU [0m[0002] Created root filesystem for container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 at /tmp/eae/containers/storage/vfs/dir/6493d899b4a3aa9facb67ec96a1ba381c135c5003b384ac6da1af433d816714f
[37mDEBU [0m[0002] /etc/system-fips does not exist on host, not mounting FIPS mode secret
[37mDEBU [0m[0002] reading hooks from /etc/containers/oci/hooks.d
[37mDEBU [0m[0002] added hook /etc/containers/oci/hooks.d/oci-nvidia-hook.json
[37mDEBU [0m[0002] hook oci-nvidia-hook.json matched; adding to stages [prestart]
[37mDEBU [0m[0002] Created OCI spec for container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 at /tmp/eae/containers/storage/vfs-containers/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6/userdata/config.json
[37mDEBU [0m[0002] /usr/libexec/podman/conmon messages will be logged to syslog
[37mDEBU [0m[0002] running conmon: /usr/libexec/podman/conmon     [37margs [0m="[-c 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 -u 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 -n dazzling_cartwright -r /usr/lib/cri-o-runc/sbin/runc -b /tmp/eae/containers/storage/vfs-containers/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6/userdata -p /run/user/2018/vfs-containers/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6/userdata/pidfile --exit-dir /run/user/2018/libpod/tmp/exits --conmon-pidfile /run/user/2018/vfs-containers/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6/userdata/conmon.pid --exit-command /usr/bin/podman --exit-command-arg --root --exit-command-arg /tmp/eae/containers/storage --exit-command-arg --runroot --exit-command-arg /run/user/2018 --exit-command-arg --log-level --exit-command-arg debug --exit-command-arg --cgroup-manager --exit-command-arg cgroupfs --exit-command-arg --tmpdir --exit-command-arg /run/user/2018/libpod/tmp --exit-command-arg --runtime --exit-command-arg runc --exit-command-arg --storage-driver --exit-command-arg vfs --exit-command-arg container --exit-command-arg cleanup --exit-command-arg --rm --exit-command-arg 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 --socket-dir-path /run/user/2018/libpod/tmp/socket -l k8s-file:/tmp/eae/containers/storage/vfs-containers/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6/userdata/ctr.log --log-level debug --syslog]"
[33mWARN [0m[0002] Failed to add conmon to cgroupfs sandbox cgroup: error creating cgroup for cpuset: mkdir /sys/fs/cgroup/cpuset/libpod_parent: permission denied
[conmon:d]: failed to write to /proc/self/oom_score_adj: Permission denied

[37mDEBU [0m[0003] Received container pid: 181118              
[37mDEBU [0m[0003] Created container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 in OCI runtime
[37mDEBU [0m[0003] Attaching to container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6
[37mDEBU [0m[0003] connecting to socket /run/user/2018/libpod/tmp/socket/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6/attach
[37mDEBU [0m[0003] Starting container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 with command [nvidia-smi]
[37mDEBU [0m[0003] Started container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6
Mon Oct 14 17:18:44 2019      
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 410.104      Driver Version: 410.104      CUDA Version: 10.0     |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  Tesla K80           On   | 00000002:03:00.0 Off |                    0 |
| N/A   32C    P8    26W / 149W |      0MiB / 11441MiB |      2%      Default |
+-------------------------------+----------------------+----------------------+
[37mDEBU [0m[0003] Enabling signal proxying                    
|   1  Tesla K80           On   | 00000002:04:00.0 Off |                    0 |
| N/A   29C    P8    31W / 149W |      0MiB / 11441MiB |      2%      Default |
+-------------------------------+----------------------+----------------------+
                                                                               
+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID   Type   Process name                             Usage      |
|=============================================================================|
|  No running processes found                                                 |
+-----------------------------------------------------------------------------+
[37mDEBU [0m[0004] Checking container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 status...
[37mDEBU [0m[0004] Attempting to read container 427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6 exit code from file /run/user/2018/libpod/tmp/exits/427b4716bca98d8f83fbe6b18095840f75faf8217d5b3e685505ec19c92c21d6-old
[37mDEBU [0m[0004] [graphdriver] trying provided driver "vfs"  
]0;eae@f12n13: /home/eae eae@f12n13:~$ exit

Script done on 2019-10-14 13:18:47-0400