Last time we talked about how /proc has directories for each process but that there were also some files in that directory.  This time we’ll talk about a couple of those files.  /proc and its files have lots of information about the running of your system.

Let’s start with meminfo.  That’s a weird name, right?  Well, surprise, surprise, it has something to do with memory.  It has the current state of the memory on your system.

MemTotal:       32953488 kB
MemFree:        12891648 kB
Buffers:           56460 kB
Cached:          7736136 kB
SwapCached:       720288 kB
Active:         12263732 kB
Inactive:        5540668 kB
Active(anon):    9316432 kB
Inactive(anon):  3067828 kB
Active(file):    2947300 kB
Inactive(file):  2472840 kB
Unevictable:       26100 kB
Mlocked:           15880 kB
SwapTotal:       3117180 kB
SwapFree:        1736868 kB
Dirty:              1820 kB
Writeback:             0 kB
AnonPages:       9560840 kB
Mapped:          2414060 kB
Shmem:           2369068 kB
Slab:             768816 kB
SReclaimable:     521000 kB
SUnreclaim:       247816 kB
KernelStack:       18416 kB
PageTables:       365784 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    19593924 kB
Committed_AS:   27252100 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      276548 kB
VmallocChunk:   34359361512 kB
AnonHugePages:    491520 kB
DirectMap4k:        7488 kB
DirectMap2M:     4179968 kB
DirectMap1G:    29360128 kB

That’s a lot of information and we don’t really care what it all means.  The first two lines are the interesting part, they tell us the total memory on the system (in kilobytes). This system has 32 Gigabytes of memory installed on it and 39% of it is being used.  (I figured that out by dividing the amount of memory being used by the memory on the system).

Another file is the devices file.  That’s a list of devices on the system.  Remember, /dev/  has a list of all possible devices, the devices file in /proc has a list of all the devices on the system.  I can cat that one and see:

Character devices:
  1 mem
  2 pty
  3 ttyp
  4 /dev/vc/0
  4 tty
  5 /dev/tty
  5 /dev/console
  5 /dev/ptmx
  7 vcs
 10 misc
 13 input
108 ppp
128 ptm
136 pts
229 hvc
254 uio

Block devices:
  1 ramdisk
259 blkext
  7 loop
  9 md
 43 nbd
147 drbd
202 xvd
253 device-mapper
254 mdp

So the question now is, what’s a block device and what’s a character device?  Tune in next time for more information… Same bat time, same bat station!

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©.

Way back at the beginning I said that Linux® treats everything as a file.  Everything!  That includes devices, like the network interface, the wireless interface, the USB port, the motherboard, the sound board, speakers, microphones, you get the idea.  Every device you could add to your computer is treated like a file.

We can’t have those files floating around willy nilly, can we?  That’d be very confusing very quickly.  Sort of like asking the Hulk to keep track of Hawkeye’s arrows.  it would go really badly.

Hawkeye

Instead, Linux® keeps all those files in one place, known as the /dev directory.  Every device has a file in this directory that Linux® uses to communicate with it.

If I do ls -l on /dev I get 676 lines.  I know because I did this:

Alpha:~ computerlamp$ ls -l /dev |  wc -l 
676

That doesn’t mean there are 676 devices on my system!  I’d have one busy system if that was the case.   It means that there are the possibilities for that many devices.

Let’s look at some of the output from ls -l:

Alpha:~ computerlamp$ ls -l /dev/
crw------- 1 root root  10, 235 Aug 11 02:19 autofs
crw------- 1 root root   5,   1 Aug 11 02:19 console
lrwxrwxrwx 1 root root       11 Aug 11 02:19 core -> /proc/kcore
crw------- 1 root root  10,  58 Aug 11 02:19 cpu_dma_latency
drwxr-xr-x 3 root root       60 Aug 11 02:19 disk
crw------- 1 root root  10,  63 Aug 11 02:19 dlm-control
crw------- 1 root root  10,  62 Aug 11 02:19 dlm-monitor
crw------- 1 root root  10,  61 Aug 11 02:19 dlm_plock
crw------- 1 root root  10,  60 Aug 11 02:19 ecryptfs
lrwxrwxrwx 1 root root       13 Aug 11 02:19 fd -> /proc/self/fd
crw-rw-rw- 1 root root   1,   7 Aug 11 02:19 full
crw------- 1 root root  10, 229 Aug 11 02:19 fuse

That isn’t very helpful, is it.  I don’t know what dlm means and why there’s a dlm-control or a dlm-monitor  I’m going to guess that the disk directory has something to do with hard drives, but I’m not sure.  encryptfs looks interesting, I bet it has something to do with encrypting things, but I’m not sure of that either.

The other thing to pay attention to is that the ownership and permissions of a lot of the files in this directory are restricted to root.  That means that while I can use ls -l to see that they’re there, I can’t actually look at them.