Bash
About Bash
In addition to the NX-OS CLI, Cisco Nexus 3000 Series devices support access to the Bourne-Again SHell (Bash). Bash interprets commands that you enter or commands that are read from a shell script. Using Bash enables access to the underlying Linux system on the device and to manage the system.
Accessing Bash
In Cisco NX-OS, Bash is accessible from user accounts that are associated with the Cisco NX-OS dev-ops role or the Cisco NX-OS network-admin role.
The following example shows the authority of the dev-ops role and the network-admin role:
switch# show role name dev-ops Role: dev-ops Description: Predefined system role for devops access. This role cannot be modified. Vlan policy: permit (default) Interface policy: permit (default) Vrf policy: permit (default) ------------------------------------------------------------------- Rule Perm Type Scope Entity ------------------------------------------------------------------- 4 permit command conf t ; username * 3 permit command bcm module * 2 permit command run bash * 1 permit command python *
switch# show role name network-admin Role: network-admin Description: Predefined network admin role has access to all commands on the switch ------------------------------------------------------------------- Rule Perm Type Scope Entity ------------------------------------------------------------------- 1 permit read-write switch#
Bash is enabled by running the feature bash-shell command.
The run bash command loads Bash and begins at the home directory for the user.
The following examples show how to enable the Bash shell feature and how to run Bash.
switch# configure terminal switch(config)# feature bash-shell
switch# run bash Linux# whoami admin Linux# pwd /bootflash/home/admin Linux#
 Note | You can also execute Bash commands with the run bash <command> command. The following is an example of the run bash <command> command. run bash whoami |
Escalate Privileges to Root
The privileges of an admin user can escalate their privileges for root access.
The following are guidelines for escalating privileges:
-
Only an admin user can escalate privileges to root.
-
Bash must be enabled before escalating privileges.
-
Escalation to root is password protected.
The following example shows how to escalate privileges to root and how to verify the escalation:
switch# run bash
Linux# sudo su root
We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:
#1) Respect the privacy of others.
#2) Think before you type.
#3) With great power comes great responsibility.
Password:
Linux# whoami
root
Linux# exit
exit
Examples of Bash Commands
This section contains examples of Bash commands and output.
Displaying System Statistics
The following example shows how to display system statistics:
switch# run bash Linux# cat /proc/meminfo MemTotal: 3795100 kB MemFree: 1472680 kB Buffers: 136 kB Cached: 1100116 kB ShmFS: 1100116 kB Allowed: 948775 Pages Free: 368170 Pages Available: 371677 Pages SwapCached: 0 kB Active: 1198872 kB Inactive: 789764 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 0 kB Writeback: 0 kB AnonPages: 888272 kB Mapped: 144044 kB Slab: 148836 kB SReclaimable: 13892 kB SUnreclaim: 134944 kB PageTables: 28724 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 1897548 kB Committed_AS: 19984932 kB VmallocTotal: 34359738367 kB VmallocUsed: 215620 kB VmallocChunk: 34359522555 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 40960 kB DirectMap2M: 4190208 kB Linux#
Running Bash from CLI
The following example shows how to run a bash command from the CLI with the run bash <command> command:
switch# run bash ps -el F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD 4 S 0 1 0 0 80 0 - 497 select ? 00:00:08 init 5 S 0 2 0 0 75 -5 - 0 kthrea ? 00:00:00 kthreadd 1 S 0 3 2 0 -40 - - 0 migrat ? 00:00:00 migration/0 1 S 0 4 2 0 75 -5 - 0 ksofti ? 00:00:01 ksoftirqd/0 5 S 0 5 2 0 58 - - 0 watchd ? 00:00:00 watchdog/0 1 S 0 6 2 0 -40 - - 0 migrat ? 00:00:00 migration/1 1 S 0 7 2 0 75 -5 - 0 ksofti ? 00:00:00 ksoftirqd/1 5 S 0 8 2 0 58 - - 0 watchd ? 00:00:00 watchdog/1 1 S 0 9 2 0 -40 - - 0 migrat ? 00:00:00 migration/2 1 S 0 10 2 0 75 -5 - 0 ksofti ? 00:00:00 ksoftirqd/2 5 S 0 11 2 0 58 - - 0 watchd ? 00:00:00 watchdog/2 1 S 0 12 2 0 -40 - - 0 migrat ? 00:00:00 migration/3 1 S 0 13 2 0 75 -5 - 0 ksofti ? 00:00:00 ksoftirqd/3 5 S 0 14 2 0 58 - - 0 watchd ? 00:00:00 watchdog/3 ... 4 S 0 8864 1 0 80 0 - 2249 wait ttyS0 00:00:00 login 4 S 2002 28073 8864 0 80 0 - 69158 select ttyS0 00:00:00 vsh 4 R 0 28264 3782 0 80 0 - 54790 select ? 00:00:00 in.dcos-telnet 4 S 0 28265 28264 0 80 0 - 2247 wait pts/0 00:00:00 login 4 S 2002 28266 28265 0 80 0 - 69175 wait pts/0 00:00:00 vsh 1 S 2002 28413 28266 0 80 0 - 69175 wait pts/0 00:00:00 vsh 0 R 2002 28414 28413 0 80 0 - 887 - pts/0 00:00:00 ps switch#
Running Python from Bash
The following example shows how to load Python and configure a switch using Python objects:
switch# run bash
Linux# python
Python 2.7.5 (default, May 16 2014, 10:58:01)
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
Loaded cisco NxOS lib!
>>>
>>> from cisco import *
>>> from cisco.vrf import *
>>> from cisco.interface import *
>>> vrfobj=VRF('myvrf')
>>> vrfobj.get_name()
'myvrf'
>>> vrfobj.add_interface('Ethernet1/3')
True
>>> intf=Interface('Ethernet1/3')
>>> print intf.config()
!Command: show running-config interface Ethernet1/3
!Time: Thu Aug 21 23:32:25 2014
version 6.0(2)U4(1)
interface Ethernet1/3
no switchport
vrf member myvrf
>>>
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