When I list /proc/<PID>, works as expected. But when I use ps or ls /proc | grep <PID>, the process is hidden. How & Why is this possible?[user@host ~]$ ls /proc/12263attr             cpuset   limits      net            projid_map  statmautogroup        cwd      loginuid    ns             root        statusauxv             environ  map_files   numa_maps      sched       syscallcgroup           exe      maps        oom_adj        sessionid   taskclear_refs       fd       mem         oom_score      setgroups   timerscmdline          fdinfo   mountinfo   oom_score_adj  smaps       uid_mapcomm             gid_map  mounts      pagemap        stack       wchancoredump_filter  io       mountstats  personality    stat[user@host ~]$ ls /proc | grep 12212230122311226012297[user@host ~]$ ls /proc/12263attr             cpuset   limits      net            projid_map  statmautogroup        cwd      loginuid    ns             root        statusauxv             environ  map_files   numa_maps      sched       syscallcgroup           exe      maps        oom_adj        sessionid   taskclear_refs       fd       mem         oom_score      setgroups   timerscmdline          fdinfo   mountinfo   oom_score_adj  smaps       uid_mapcomm             gid_map  mounts      pagemap        stack       wchancoredump_filter  io       mountstats  personality    stat[user@host ~]$ ls /proc | grep 12212230122311226012297[user@host ~]$ ps -fp 12263UID        PID  PPID  C STIME TTY          TIME CMD[user@host ~]$ 
Inconsistent output on /proc. Can some processes be hidden?
process;proc