The Xen basic commands very helpful for manage virtual machine like, available RAM space, start, stop, pause, unpause and etc.

XEN command syntax is: 

xm [ xen-name (or) id ]

1. XEN Machine Information:

Get the information about Xen release, version, free memory space in server and etc,

# xm info

host                   : hostname.xenserver
release                : 3.14.13-1.el6xen.x86_64
version                : #1 SMP Sun May 11 12:44:21 EST 2014
machine                : x86_64
nr_cpus                : 24
nr_nodes               : 2
cores_per_socket       : 6
threads_per_core       : 2
cpu_mhz                : 2100
virt_caps              : hvm
total_memory           : 15711
free_memory            : 10936
free_cpus              : 0
xen_major              : 4
xen_minor              : 2
xen_extra              : .4
xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32 hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler          : credit
xen_pagesize           : 4096
platform_params        : virt_start=0xffff800000000000
xen_changeset          : unavailable
xen_commandline        : dom0_mem=3144M
cc_compiler            : gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4)
cc_compile_by          : mockbuild
cc_compile_domain      : crc.id.au
cc_compile_date        : Wed Jun 18 01:34:43 EST 2014
xend_config_format     : 4

2. Startup virtual machine:

# xm create /xen/testing.cfg

Using config file "/xen/testing.cfg".
Using to parse /boot/grub/grub.conf
Started domain testing

3. View virtual machine's console:

# xm console  testing

                Welcome to CentOS
Starting udev: udev: starting version 147
Initialising Xen virtual ethernet driver.
[  OK  ]

It will ask login name and password,

host.testing.com login: root
Password:
Last login: Wed Aug  6 17:44:00 from 122.178.83.211

If you want to exit from the virtual console press CTRL + }

4. Display Active/Inactive  virtual machine's:


List of virtual server names, ID, RAM memory allocation, states and running time duration,

# xm list

Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0  6144    24     r-----    140.8
brdemo                                           256     1                 0.0
demo2                                        1   256     1     -b----     14.8
demo3                                        2  1024     1     -b----     14.6
demo5                                           1024     1                13.5

5. Shut down, Destroy, Pause, Unpause, Reboot a virtual machine:

# xm shutdown xenname

The system is going down for power off NOW!
Stopping atd: [  OK  ]
Stopping sshd: [  OK  ]
Shutting down exim: [  OK  ]
Shutting down spamd: [FAILED]
...
init: Re-executing /sbin/init
JBD: barrier-based sync failed on xvda1 - disabling barriers
Halting system...
md: stopping all md devices.
System halted.

Destroy command is terminate a virtual machine same as to power off
# xm destroy xenname

Reboot command is restart your virtual machine
# xm reboot xenname

The below commands are temporarily pause and unpause execution virtual machine.

# xm pause xenname

# xm unpause xenname

6. Get Uptime  a virtual Machine:

# xm uptime testing
Name                              ID Uptime
testing                          310  0:20:03

7. Get the State of a Virtual Machine:

# xm domstate demo3
idle

# xm domstate demo5
shutoff

8. View log:

# xm log

9. Different views xm top command:
# xm top

command, which provides real time monitoring of domains.  if you want exit from monitoring press ctrl+c  or press shift + Q

xentop - 15:45:55   Xen 4.2.4
3 domains: 1 running, 2 blocked, 0 paused, 0 crashed, 0 dying, 0 shutdown
Mem: 15253542k total, 6582352k used, 20352565k free    CPUs: 24 @ 2100MHz
      NAME  STATE   CPU(sec) CPU(%)     MEM(k) MEM(%)  MAXMEM(k) MAXMEM(%) VCPUS NETS NETTX(k) NETRX(k) VBDS   VBD_OO   VBD_RD   VBD_WR  VBD_RSECT  VB
D_WSECT SSID
     demo2 --b---         15    0.0     262144    0.8    4194304      12.5     1    1       228       92    2        0     2191      295      81436
   2712    0
     demo3 --b---         14    0.0    1048576    3.1    4194304      12.5     1    1       221       89    2        0     2139      246      79980
   2192    0
  Domain-0 -----r        155    1.8    6291456   18.8   no limit       n/a    24    0        0        0    0        0        0        0         0
      0    0

  Delay  Networks  vBds  Tmem  VCPUs  Repeat header  Sort order  Quit

VCPUs

View the virtual server by VCPU's press Shift+V

xentop - 15:46:35   Xen 4.2.4
3 domains: 1 running, 2 blocked, 0 paused, 0 crashed, 0 dying, 0 shutdown
Mem: 15253542k total, 6582352k used, 20352565k free    CPUs: 24 @ 2100MHz
      NAME  STATE   CPU(sec) CPU(%)     MEM(k) MEM(%)  MAXMEM(k) MAXMEM(%) VCPUS NETS NETTX(k) NETRX(k) VBDS   VBD_OO   VBD_RD   VBD_WR  VBD_RSECT  VB
D_WSECT SSID
     demo2 --b---         15    0.0     262144    0.8    4194304      12.5     1    1       231       92    2        0     2191      298      81436
   2736    0
VCPUs(sec):   0:         15s
     demo3 --b---         14    0.0    1048576    3.1    4194304      12.5     1    1       224       89    2        0     2139      246      79980
   2192    0
VCPUs(sec):   0:         14s
  Domain-0 -----r        155    1.8    6291456   18.8   no limit       n/a    24    0        0        0    0        0        0        0         0
      0    0
VCPUs(sec):   0:         17s  1:          2s  2:          5s  3:          4s  4:         20s
          5:          2s  6:          8s  7:          1s  8:          8s  9:          1s
         10:          6s 11:          1s 12:          9s 13:          2s 14:          6s
         15:          5s 16:         17s 17:          2s 18:          9s 19:          2s
         20:         11s 21:          1s 22:          5s 23:          1s

  Delay  Networks  vBds  Tmem  VCPUs  Repeat header  Sort order  Quit 

Network:

View the virtual server by networks press Shift+N

xentop - 15:46:58   Xen 4.2.4
3 domains: 1 running, 2 blocked, 0 paused, 0 crashed, 0 dying, 0 shutdown
Mem: 15253542k total, 6582352k used, 20352565k free    CPUs: 24 @ 2100MHz
      NAME  STATE   CPU(sec) CPU(%)     MEM(k) MEM(%)  MAXMEM(k) MAXMEM(%) VCPUS NETS NETTX(k) NETRX(k) VBDS   VBD_OO   VBD_RD   VBD_WR  VBD_RSECT  VB
D_WSECT SSID
     demo2 --b---         15    0.0     262144    0.8    4194304      12.5     1    1       234       92    2        0     2191      298      81436
   2736    0
Net0 RX:    94793bytes      636pkts        0err        0drop  TX:   239718bytes     1752pkts        0err        0drop
     demo3 --b---         14    0.0    1048576    3.1    4194304      12.5     1    1       226       89    2        0     2139      249      79980
   2216    0
Net0 RX:    91240bytes      576pkts        0err        0drop  TX:   232064bytes     1695pkts        0err        0drop
  Domain-0 -----r        156    1.0    6291456   18.8   no limit       n/a    24    0        0        0    0        0        0        0         0
      0    0

  Delay  Networks  vBds  Tmem  VCPUs  Repeat header  Sort order  Quit 

Refresh your xm top report at every 5 seconds, press Shift+D and enter your seconds value.
 
  Delay(sec): 5

10. To Display Virtual CPU assignments:

# xm vcpu-list

Name                              ID VCPUs   CPU State   Time(s) CPU Affinity
Domain-0                           0     0     0   ---  1671261.0 0
Domain-0                           0     1     1   -b-  185739.8 1
Domain-0                           0     2     2   -b-   42527.0 2
Domain-0                           0     3     3   -b-   38464.6 3
Domain-0                           0     4     4   -b-  115936.5 4
Domain-0                           0     5     5   -b-   38494.7 5
Domain-0                           0     6     6   -b-   39606.2 6
Domain-0                           0     7     7   -b-   37916.3 7
Domain-0                           0     8     8   r--   38504.9 8
Domain-0                           0     9     9   -b-   38227.8 9
Domain-0                           0    10    10   -b-   37479.2 10
Domain-0                           0    11    11   -b-   36470.3 11
brdemo                            275     0     0   -b-  252823.9 any cpu
demo2                              47     0     5   -b-  1190015.7 any cpu
demo3                            103     0     2   -b-  330218.0 any cpu
demo5                            278     0     0   -b-   88573.2 any cpu

11. More XEN commands,

If you will give xm command with any subcommand shows the common xm commands,

# xm

Usage: xm [args]

Control, list, and manipulate Xen guest instances.

Common 'xm' commands:

 console              Attach to 's console.                     
 vncviewer            Attach to 's VNC server.                  
 create               Create a domain based on .            
 new                  Adds a domain to Xend domain management           
 delete               Remove a domain from Xend domain management.      
 destroy              Terminate a domain immediately.                   
 dump-core            Dump core for a specific domain.                  
 help                 Display this message.                             
 list                 List information about all/some domains.          
 mem-set              Set the current memory usage for a domain.        
 migrate              Migrate a domain to another machine.              
 pause                Pause execution of a domain.                      
 reboot               Reboot a domain.                                  
 reset                Reset a domain.                                   
 restore              Restore a domain from a saved state.              
 resume               Resume a Xend managed domain                      
 save                 Save a domain state to restore later.             
 shell                Launch an interactive shell.                      
 shutdown             Shutdown a domain.       

I hope you this post very helped for you.