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Full Discussion: Process existence or/and permission
Top Forums Shell Programming and Scripting Process existence or/and permission Post 302999920 by chebarbudo on Friday 30th of June 2017 04:28:23 AM
Old 06-30-2017
When I don't know how to undo something, I often search how to DO it. It worked today with linux hide processes from other users - Recherche Google.
So if hidepid allows you to hide processes, it should do the opposite if deactivated.
Apparently hidepid is not in use though and I can only see 4 processes wether I use ls /proc or ps:
Code:
santiago@alphard:~$ sudo mount | grep proc
proc on /proc type proc (rw,relatime)
santiago@alphard:~$ ls -ld /proc/{0..9}* 2> /dev/null | wc -l
4
santiago@alphard:~$ ps x -o pid= | wc -l
4

But I'm still going to try to tweak hidepid and indeed I can see more processes with ls /proc but not with ps:
Code:
santiago@alphard:~$ sudo mount -o remount,hidepid=1 /proc
santiago@alphard:~$ sudo mount | grep proc
proc on /proc type proc (rw,relatime,hidepid=1)
santiago@alphard:~$ ls -ld /proc/{0..9}* 2> /dev/null | wc -l
202
santiago@alphard:~$ ps x -o pid= | wc -l
4

Surprisingly, hidepid level 1 gives me more permission but levels 0 and 2 are exactly the same:
Code:
santiago@alphard:~$ (echo -e "mount opt\tls /proc\tps" | sed 'p;s/[^\t]/-/g'; for h in 0 1 2; do echo -e "hidepid=$h\t$(sudo mount -o remount,hidepid=$h /proc; ls -ld /proc/{0..9}* 2> /dev/null | wc -l)\t$(ps x -o pid= | wc -l)"; done) | column -tns$'\t'
mount opt  ls /proc  ps
---------  --------  --
hidepid=0  7         7
hidepid=1  201       7
hidepid=2  7         7

I'm still investigating but level 0 should give me all permissions like in old behavior.
 

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LEARN ABOUT PLAN9

lsns

LSNS(8) 						       System Administration							   LSNS(8)

NAME

       lsns - list namespaces

SYNOPSIS

       lsns [options] [namespace]

DESCRIPTION

       lsns  lists  information  about all the currently accessible namespaces or about the given namespace.  The namespace identifier is an inode
       number.

       The default output is subject to change.  So whenever possible, you should avoid using default outputs in your scripts.	Always	explicitly
       define expected columns by using the --output option together with a columns list in environments where a stable output is required.

       Note  that lsns reads information directly from the /proc filesystem and for non-root users it may return incomplete information.  The cur-
       rent /proc filesystem may be unshared and affected by a PID namespace (see unshare --mount-proc for more details).  lsns is not able to see
       persistent namespaces without processes where the namespace instance is held by a bind mount to /proc/pid/ns/type.

OPTIONS

       -J, --json
	      Use JSON output format.

       -l, --list
	      Use list output format.

       -n, --noheadings
	      Do not print a header line.

       -o, --output list
	      Specify which output columns to print.  Use --help to get a list of all supported columns.

	      The default list of columns may be extended if list is specified in the format +list (e.g. lsns -o +PATH).

       -p, --task pid
	      Display only the namespaces held by the process with this pid.

       -r, --raw
	      Use the raw output format.

       -t, --type type
	      Display  the  specified type of namespaces only.	The supported types are mnt, net, ipc, user, pid, uts and cgroup.  This option may
	      be given more than once.

       -u, --notruncate
	      Do not truncate text in columns.

       -V, --version
	      Display version information and exit.

       -h, --help
	      Display help text and exit.

AUTHORS

       Karel Zak <kzak@redhat.com>

SEE ALSO

       nsenter(1), unshare(1), clone(2), namespaces(7)

AVAILABILITY

       The lsns command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux							   December 2015							   LSNS(8)
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