Everything is awesome! I mean, in Linux, everything is a file! We even saw where devices are files. But we also have processes, things that run and do things. Are they files? Well, the answer is… (drum roll)…yes. Everything is a file. Where devices are in /dev, process are in /proc. That kind of makes sense, right?

If you ls /, the top directory on your system, you’ll see something like:

bin   dev  home  lost+found  misc  net  opt   root  selinux  sys  usr
boot  etc  lib   media       mnt   od   proc  sbin  srv      tmp  var

So let’s cd into /proc and look around:

1     13     19     2705  2957   328  6          devices      kmsg          softirqs
10    14     2      2769  2972   329  6960       diskstats    kpagecount    stat
1013  14761  20     2771  2985   33   6962       dma          kpageflags    swaps
1043  14766  21     2791  2986   330  6963       drbd         loadavg       sys
1067  15     22     2794  2988   331  7          driver       locks         sysrq-trigger
1076  158    23     28    3      332  8          execdomains  mdstat        sysvipc
1095  16     24     2803  314    333  9          filesystems  meminfo       timer_list
11    160    24853  2841  315    334  901        fs           misc          tty
1102  162    25     2882  316    335  buddyinfo  interrupts   modules       uptime
1150  17     25077  29    320    336  bus        iomem        mounts        version
1152  171    25265  2901  32082  337  cmdline    ioports      net           vmallocinfo
1153  1743   255    2915  322    338  config.gz  irq          pagetypeinfo  vmstat
1161  1745   257    2932  325    339  consoles   kallsyms     partitions    zoneinfo
1173  1746   26     2940  326    34   cpuinfo    kcore        self
12    18     27     2949  327    5    crypto     key-users    slabinf

The numbers in proc correspond to processes that are currently running on your Linux system. On this system, there’s a process numbered 29 and one numbered 2901. There’s even 1150, 1152 and 1153. This system isn’t that busy, there’s only 98 processes currently running on it. That may seem like a lot, but a busy web server or a busy mail server could have a thousand busy processes.

Each one of those numbers is a directory and in that directory are files (see what I did there) that are information for that process. I looked in /proc/1 and saw:

ls: cannot read symbolic link 1/cwd: Permission denied
ls: cannot read symbolic link 1/root: Permission denied
ls: cannot read symbolic link 1/exe: Permission denied
attr/       coredump_filter  fdinfo/   mem         oom_adj        root@      status
auxv        cwd@             io        mountinfo   oom_score      sessionid  syscall
clear_refs  environ          limits    mounts      oom_score_adj  smaps      task/
cmdline     exe@             loginuid  mountstats  pagemap        stat       wchan
comm        fd/              maps      net/        personality    statm

What do those first three lines mean? Well, they mean I don’t really have permission to loo at everything in this directory. I could see that further if I did an <b>ls -l</b> on it, but this is really just to show you what’s in the directory.

Next time we’ll talk about some of the files in the /proc directory.

Back in this post I said ‘there’s more than one way to do it’ should be a motto of Linux©.  We’re going to do it again, this time with memory.  There’s another way to do it.

There’s the free command that shows you how much you have:

Alpha:~ computerlamp$ free
             total       used       free     shared    buffers     cached
Mem:        509688     491316      18372          0      97264     208964
-/+ buffers/cache:     185088     324600
Swap:       262140        316     261824

And we can give it a flag to show that information in gigabytes:

Alpha:~ computerlamp$ free -g
             total       used       free     shared    buffers     cached
Mem:             0          0          0          0          0          0
-/+ buffers/cache:          0          0
Swap:            0          0          0

Wait, something’s wrong.  There’s no memory on this system?  Well, it turns out that this one is an older Alpha.  (I logged into the wrong system this morning) and it doesn’t even have a gigabyte of memory.  I have to give it the -m flag.

Alpha:~ computerlamp$ free -m
             total       used       free     shared    buffers     cached
Mem:           497        479         18          0         94        204
-/+ buffers/cache:        180        317
Swap:          255          0        255

I really should have logged into the new Alpha and not the old one.

Anyway, back to the old Alpha.  There’s another way to look at memory, this time we use the command vmstat.

Alpha:~ computerlamp$ vmstat
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0    316  18488  97276 209068    0    0     0     0    1    1  0  0 100  0  0

The columns under the memory tag show us how much we have sitting around.

So, there’s another way.  Always another way in Linux©.