This article provides an example explaining the outcome when upgrading Junos OS with the unlink option.

For a similar example using the no-copy option, see KB32190 - Example - Upgrade Junos OS with no-copy option on SRX [juniper.net] .
For a similar example using the partition option, see KB32192 - Example - Upgrade Junos OS with partition option on SRX [juniper.net] .

Note: The Installation and Upgrade Guide provides an example of the common method to upgrade Junos OS on SRX devices ; however, if your installation requires using different options, these examples explain the outcome.

Below is the example output when upgrading Junos OS with the unlink option, on SRX branch devices.

Junos OS Upgrade With unlink Option

root@SRX-345> show version
Hostname: SRX-345-2
Model: srx345
Junos: 15.1X49-D70.3
JUNOS Software Release [15.1X49-D70.3]

root@SRX-345> show system snapshot media internal
Information for snapshot on       internal (/dev/da0s1a) (primary)
Creation date: Sep 15 03:08:37 2017
JUNOS version on snapshot:
  junos  : 15.1X49-D70.3-domestic
Information for snapshot on       internal (/dev/da0s2a) (backup)
Creation date: Sep 15 03:54:37 2017
JUNOS version on snapshot:
  junos  : 15.1X49-D70.3-domestic
 
root@SRX-345> file list /var/tmp/install/
 
/var/tmp/install/:
junos-srxsme-15.1X49-D110.4-domestic.tgz  <<<<<<<<<<Install package was copied to /var/tmp/install
</span>

root@SRX-345> request system software add no-validate no-copy unlink /var/tmp/install/junos-srxsme-15.1X49-D110.4-domestic.tgz
                      
Formatting alternate root (/dev/da0s2a)...
/dev/da0s2a: 2518.0MB (5156848 sectors) block size 16384, fragment size 2048
        using 14 cylinder groups of 183.62MB, 11752 blks, 23552 inodes.
super-block backups (for fsck -b #) at:
 32, 376096, 752160, 1128224, 1504288, 1880352, 2256416, 2632480, 3008544,
 3384608, 3760672, 4136736, 4512800, 4888864
Removing              /var/tmp/install/junos-srxsme-15.1X49-D110.4-domestic.tgz
Installing package '/altroot/cf/packages/install-tmp/junos-15.1X49-D110.4-domestic' ...
Verified junos-boot-srxsme-15.1X49-D110.4.tgz signed by PackageProductionEc_2017 method ECDSA256+SHA256
Verified junos-srxsme-15.1X49-D110.4-domestic signed by PackageProductionEc_2017 method ECDSA256+SHA256
JUNOS 15.1X49-D110.4 will become active at next reboot
Saving state for rollback ...
Rebooting ...
shutdown: [pid 2852]
Shutdown NOW!                                                                            
*** FINAL System shutdown message from root@SRX-345-2 ***                   
System going down IMMEDIATELY  

The install package is removed from the folder after finishing the upgrade.

root@SRX-345> show version 
Hostname: SRX-345-2
Model: srx345
Junos: 15.1X49-D110.4
JUNOS Software Release [15.1X49-D110.4]
 
root@SRX-345> show system snapshot media internal
Information for snapshot on       internal (/dev/da0s1a) (backup)
Creation date: Sep 14 10:36:55 2017
JUNOS version on snapshot:
  junos  : 15.1X49-D70.3-domestic
Information for snapshot on       internal (/dev/da0s2a) (primary)
Creation date: Sep 15 04:28:56 2017
JUNOS version on snapshot:
  junos  : 15.1X49-D110.4-domestic
 
root@SRX-345> file list /var/tmp/install/

2020-06-24: Article reviewed for accuracy; no changes required. Article is correct and complete.