The following error is displayed on NetScaler SDX SVM:
System maintenance in progress. Please try after some time

It is a known issue. You need to upgrade to 10.5 59.x and reboot the SVM for fixing it with the current version.

Rebooting the SVM does not bring down the NetScaler VPX instances running on SDX.

Follow the steps as below to reboot the SVM:

1. Log in to XenServer with root user and password.

2. Run the following command from shell session on the XenServer:
   xe vm-list
   Note the uuid from above command output for the Management Service VM

3. Then run the below reboot command for the SVM instance:
   xe vm-reboot uuid=<uuid>

4. You can check the status of the SVM, by pinging the IP, running the xe vm-list command again, or consoling into it by following CTX136121

Once there is access to the SVM, we can look for the "out of swap space" error in SVM logs under /var/log/messages as below:

Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(14): failed Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(15): failed Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(12): failed Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(9): failed

Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(16): failed
Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(12): failed
Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(9): failed
Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(16): failed
Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(9): failed
Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(16): failed
Oct 25 18:57:11 nssdx-mgmt kernel: swap_pager_getswapspace(3): failed 
Oct 25 18:57:11 nssdx-mgmt last message repeated 8 times
Oct 25 18:57:11 nssdx-mgmt kernel: pid 340 (svm_stat), uid 0, was killed: out of swap space
Oct 25 18:57:11 nssdx-mgmt kernel: pid 330 (svm_inventory), uid 0, was killed: out of swap space 
Oct 25 18:57:12 nssdx-mgmt svm_event: 10.242.176.12 10/25/2015:18:57:12 GMT : SNMP TRAP_SENT : 127.0.0.1:SubSystemState:svm_stat - SubSystem Down: svm_stat
Oct 25 18:57:12 nssdx-mgmt svm_event: 10.242.176.12 10/25/2015:18:57:12 GMT : EVENT SUBSYSTEMDOWN : 127.0.0.1:SubSystemState:svm_stat - SubSystem Down: svm_stat

The issue is tracked under the following bug number and release notes of 10.5-59.13 for reference to confirm the bug is fixed:
https://download.citrix.com/content/dam/citrix/en_us/documents/downloads/netscaler-adc/NS_10_5_59_13.html 

User Interface * CB management service (SVM) causes failure due to memory leak.. [# 565742, 573215, 576357]

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Problem Cause

It is a known issue with early builds of NS10.5 SVM firmware and is resolved in 10.5 59.x and onward

The following error is displayed on NetScaler SDX SVM: System maintenance in progress. Please try after some time

1) Log on to the XenServer using the root credentials. Then tried logging to the SVM through Xenserver and that gave us an error "internal authentication failed.". 

2) Type below command to get the dom id of the SVM:

xe vm-list params=name-label,dom-id name-label="Management Service VM"

The output will be like below, not down the ID for Management Service VM:

[root@netscaler-sdx ~]# xe vm-list params=name-label,dom-id name-label="Management Service VM"
name-label ( RW)    : Management Service VM
        dom-id ( RO): 1


3) Executed below command and crash the SVM:

usr/lib/xen/bin/crash_guest {domID of Management Service VM} 

4) We then got the SVM access back up. Made the same changes on the other SDX also to bring it up. 


Also we can try rebooting the SVM as mentioned below:
 

1. Log on to the XenServer using the root credentials.

2. Run the following command to get the UUID of the host machine:
   xe vm-list
   
   Output of the command will look like below:
   
   [root@netscaler-sdx ~]# xe vm-list
   uuid ( RO)           : b19e82df-b157-4f7f-81d8-6a583987e208
        name-label ( RW): Control domain on host: netscaler-sdx
       power-state ( RO): running
   
   
   uuid ( RO)           : e3b3d9d5-ef2b-6d4d-0312-c45f9eb71e43
        name-label ( RW): Management Service VM
       power-state ( RO): running
   Reboot the SVM using the following command:

3. xe vm-reboot uuid=<uuid of the Management Service VM>