Arista switches are really Linux servers optimized and programmed to be network switches. By this point in the book, that should not be a surprise, but what may be surprising is the depth to which you, the administrator, may gain access to the system.

To access bash, type the command bash from the enable prompt:

Arista-1#bash

Arista Networks EOS shell

[GAD@Arista-1 ~]$

At this point, I am within a bash shell on the switch. The prompt, by default, will be [username@hostname directory]$. In the previous example, I logged in to the switch with my username (GAD), as configured in the EOS CLI. I have not created a username in Unix; the switch took care of that for me.

At this point, I have just about all the control that I would have as a user in Linux. I am not a superuser, and my home directory is empty:

[GAD@Arista-1 ~]$ ls
[GAD@Arista-1 ~]$

I can navigate around the filesystem, just like I can on a Linux server:

[GAD@Arista-1 ~]$ cd /
[GAD@Arista-1 /]$ cd /usr/
[GAD@Arista-1 usr]$ ls
bin  etc  games  include  kerberos  lib  libexec  local  sbin  share
src  tmp

If you’re at all familiar with Linux, then you’ll be right at home in this bash shell:

[GAD@Arista-1 usr]$ ls -alh
total 0
drwxr-xr-x 13 root root  203 Oct 11 05:56 .
drwxr-xr-x 29 root root  220 Oct 27 20:41 ..
dr-xr-xr-x  2 root root  13K Oct 11 05:57 bin
drwxr-xr-x  2 root root    3 Aug 25  2009 etc
drwxr-xr-x  2 root root    3 Aug 25  2009 games
drwxr-xr-x  3 root root   53 Oct 11 05:56 include
drwxr-xr-x  3 root root   28 Oct 11 05:56 kerberos
dr-xr-xr-x 28 root root  35K Oct 11 05:57 lib
drwxr-xr-x  5 root root  377 Oct 11 05:56 libexec
drwxr-xr-x 11 root root  127 Oct 11 05:56 local
dr-xr-xr-x  2 root root 2.4K Oct 11 05:57 sbin
drwxr-xr-x 57 root root  896 Oct 11 05:57 share
drwxr-xr-x  4 root root   43 Oct 11 05:56 src
lrwxrwxrwx  1 root root   10 Oct 11 16:49 tmp -> ../var/tmp

To prove the point that an Arista switch is a Linux server with specialized interface hardware, I’ll show the network interfaces from bash:

[GAD@Arista-1 usr]$ ifconfig -a
cpu       Link encap:Ethernet  HWaddr 00:1C:73:08:FA:49
          UP BROADCAST RUNNING MULTICAST  MTU:9216  Metric:1
          RX packets:18 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1080 (1.0 KiB)  TX bytes:0 (0.0 b)

et1       Link encap:Ethernet  HWaddr 00:1C:73:08:FA:49
          UP BROADCAST RUNNING MULTICAST  MTU:9212  Metric:1
          RX packets:33944 errors:0 dropped:0 overruns:0 frame:0
          TX packets:62802 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:4209056 (4.0 MiB)  TX bytes:9981736 (9.5 MiB)

et2       Link encap:Ethernet  HWaddr 00:1C:73:08:FA:49
          UP BROADCAST MULTICAST  MTU:9212  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
[-- output truncated --]

Heck, even vmstat works:

[GAD@Arista-1 usr]$ vmstat 5 5
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     0 754368 104220 752528   0  0  0  0   16   10  8  1 91  0  0
 0  0     0 754376 104220 752548   0  0  0  0 1037 1266  8  1 91  0  0
 1  0     0 754376 104220 752548   0  0  0  0 1025 1238  7  1 91  0  0
 0  0     0 754376 104220 752548   0  0  0  0 1073 1359  8  1 91  0  0
 0  0     0 754376 104220 752548   0  0  0  0 1040 1284  7  1 91  0  0

I feel it is important to reiterate that all these Linux commands work because the Arista switch is a Linux machine. This is not a bash emulation; this is bash. It is more accurate to think that the CLI on the Arista switch is a switch OS emulation; although to be painfully accurate, that is not right either.

The CLI environment on an Arista switch is a process in Linux. We can see this from bash by executing the command, Cli. Here, I’ll spawn a CLI session, execute the CLI command, show clock, and then exit. Exiting a spawned CLI session returns me from whence I came—the bash shell:

[GAD@Arista-1 usr]$ Cli
Arista-1>
Arista-1>sho clock
Mon Nov  7 19:20:55 2011
timezone is UTC
Arista-1>exit
[GAD@Arista-1 usr]$

The Cli command has some pretty interesting options. Just like most other Linux commands, I can see them by appending --help at the command line:

 [GAD@Arista-1 usr]$ Cli --help
Usage: Cli [options]

Options:
  -h, --help            show this help message and exit
  -s SYSNAME, --sysname=SYSNAME
                        system name (default: ar)
  -k SYSDBSOCKNAME, --sysdbsockname=SYSDBSOCKNAME
                        Specify the unix domain socket of the
                        upstream Sysdb process
  -l, --standalone      run in standalone mode (without Sysdb).
                        Implies --disable-aaa
  --pdb                 run under pdb
  -c COMMAND, --command=COMMAND
                        run COMMAND non-interactively; separate
                        multiple commands with carriage returns
  -A, --disable-aaa     Do not communicate with the Aaa agent.  This
                        disables authentication, authorization and
                        accounting of commands executed in this Cli
                        instance.
  -M, --disable-automore
                        Do not apply paging filter for show commands
                        executed in this Cli instance.
  -e, --echo            echo commands when running non-interactively
  -p PRIVILEGE, --privilege=PRIVILEGE
                        Start the session with this privilege level.
                        Legal values are 0-15 (default: 1)
  -i PLUGINS, --plugin=PLUGINS
                        Load this plugin explicitly, and suppress
                        normal plugin search.  May be specified
                        repeatedly.
  -I, --no-plugins      suppress any plugins from loading
  -G, --disable-guards  Do not guard any commands.

One of the more interesting options is the -c command or --command=command choices. Using these options, I can execute CLI commands from within bash. For example, while in bash, executing Cli –c "sho ver" will spawn a CLI process, execute the CLI command show version, then exit, reporting the output to stdout:

[GAD@Arista-1 usr]$ Cli -c "sho ver"
Arista DCS-7124S-F
Hardware version:    07.00
Serial number:       JSH10426696
System MAC address:  001c.7308.fa49

Software image version: 4.8.1
Architecture:           i386
Internal build version: 4.8.1-495947.2011eric481Showstopper
Internal build ID:      b15379fb-13e9-4255-819f-e55dde3c3471

Uptime:                 1 week, 3 days, 22 hours and 46 minutes
Total memory:           2043424 kB
Free memory:            733244 kB

[GAD@Arista-1 usr]$

Because this is Linux, I can pipe other commands too. Here, I’ll use grep to only show the line containing the word “image”:

[GAD@Arista-1 usr]$ Cli -c "sho ver" | grep image
Software image version: 4.8.1

For my next trick, I’ll redirect the output to a file; but first, I need to be back in my home directory where I have write permissions:

[GAD@Arista-1 usr]$ cd ~
[GAD@Arista-1 ~]$
[GAD@Arista-1 ~]$ Cli -c "sho ver" | grep image > GAD.txt

I should now have a file in my home directory named GAD.txt that contains the output from my command. Let’s take a look:

[GAD@Arista-1 ~]$ ls
GAD.txt

Sure enough, there it is. Using cat should work, and it does:

[GAD@Arista-1 ~]$ cat GAD.txt
Software image version: 4.8.1
[GAD@Arista-1 ~]$

Be careful here though! Writing files to my home directory is great, but I learned the hard way that anything written to the filesystem does not survive a reboot.

Just as I could run a CLI command through the Cli command in Linux, I can run bash commands from the bash command in CLI. Sure, that may sound like circular logic, but let me show you what I mean.

Remember how I got into bash from CLI? I typed the command bash:

Arista-1#bash

Arista Networks EOS shell

[GAD@Arista-1 ~]$

That’s pretty cool, but what if I just need the output of a single command, and don’t want to go through the hassle of dropping into bash, executing the command and exiting again? Good news! I can execute bash commands from CLI, without actually dropping to the bash command line. All I have to do is append the Linux command I want to run.

Let’s say that I wanted to get the output of the Linux command, uname –a. To do this from CLI, all I need to do is issue the command bash uname –a. This will return the output from the Unix command to me without ever leaving CLI:

Arista-1#bash uname -a
Linux Arista-1 2.6.32.28.Ar-488566.2011fruggeri481 #1 SMP PREEMPT Thu
 Sep 29 02:20:09 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux
Arista-1#

Note that any commands you execute will be relative to your home directory. Thus, logged in as GAD, if I ask for my current directory with the Unix pwd command, I will get the following results:

Arista#bash pwd
/home/GAD

This book is loaded with examples where I use bash commands through CLI, or use the bash shell. Once you get the hang of how this works, you’ll start to appreciate the power inherent in the design of Arista switches. Once you feel the power, you’ll cringe every time you have to use another vendor’s switch.