Проверить запущена ли служба
# systemctl status systemd-tmpfiles-clean.service

* systemd-tmpfiles-clean.service - Cleanup of Temporary Directories
 Loaded: loaded (/usr/lib/systemd/system/systemd-tmpfiles-clean.service; static; vendor preset: disabled)
 Active: inactive (dead) since Пн 2019-07-15 07:47:32 MSK; 48min ago
 Docs: man:tmpfiles.d(5)
 man:systemd-tmpfiles(8)
 Process: 15891 ExecStart=/usr/bin/systemd-tmpfiles --clean (code=exited, status=0/SUCCESS)
 Main PID: 15891 (code=exited, status=0/SUCCESS)

июл 15 07:47:31 localhost.localdomain systemd[1]: Starting Cleanup of Temporary Direct.....
июл 15 07:47:32 localhost.localdomain systemd[1]: Started Cleanup of Temporary Directories.
Hint: Some lines were ellipsized, use -l to show in full.

Контрольный запуск служба очистки
# SYSTEMD_LOG_TARGET=console SYSTEMD_LOG_LEVEL=debug /usr/bin/systemd-tmpfiles --clean

Cleanup threshold for directory "/var/tmp" is Sat 2019-06-15 08:45:34.210617 MSK
Directory "/var/tmp/segments": modify time Mon 2019-07-15 08:26:50.856366 MSK is too new.