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/12263
attr cpuset limits net projid_map statm
autogroup cwd loginuid ns root status
auxv environ map_files numa_maps sched syscall
cgroup exe maps oom_adj sessionid task
clear_refs fd mem oom_score setgroups timers
cmdline fdinfo mountinfo oom_score_adj smaps uid_map
comm gid_map mounts pagemap stack wchan
coredump_filter io mountstats personality stat
[user@host ~]$ ls /proc | grep 122
12230
12231
12260
12297
[user@host ~]$ ls /proc/12263
attr cpuset limits net projid_map statm
autogroup cwd loginuid ns root status
auxv environ map_files numa_maps sched syscall
cgroup exe maps oom_adj sessionid task
clear_refs fd mem oom_score setgroups timers
cmdline fdinfo mountinfo oom_score_adj smaps uid_map
comm gid_map mounts pagemap stack wchan
coredump_filter io mountstats personality stat
[user@host ~]$ ls /proc | grep 122
12230
12231
12260
12297
[user@host ~]$ ps -fp 12263
UID PID PPID C STIME TTY TIME CMD
[user@host ~]$
