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Full Discussion: Implement ps command in C
Top Forums Programming Implement ps command in C Post 302873017 by freedombird9 on Monday 11th of November 2013 02:55:18 AM
Old 11-11-2013
Implement ps command in C

Hello, could anybody explain how the ps command works? I know something about the proc file system. But I'm still not sure about how it exactly works. Like ps without any option will print out the current user's processes, but it never displays my web browsers such as firefox or my LibreOffice while they're open.

I know all the files with numerical names are PIDs, but I don't know how the ps command differentiate them, catargorizing them according the users who fired them. Or where it gets the TTY and cpu time and CMD info.

That would be wonderful if someone could give a simple example about how to mimick the functions of ps command just by reading the proc directory(better in C). Thanks a lot.
 

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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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