Oracle Startup Error
ORA-00845: MEMORY_TARGET not supported on this system：
This occurs because the Oracle MEMORY_TARGET size was previously configured, but the shared memory (shm) size in the system is insufficient, causing the startup failure.
Solution：
vi /etc/fstab
Find the line：
tmpfs /dev/shm tmpfs defaults 0 0
Modify it to：
tmpfs /dev/shm tmpfs defaults,size=6G 0 0
#Set the size value according to your situation. It should be larger than the MEMORY_TARGET size and smaller than the total system memory.
Remount the filesystem：
mount -o remount /dev/shm
Start Oracle again：
SQL> startupORACLE instance started.Total System Global Area 3507474432 bytesFixed Size 2218352 bytesVariable Size 1056966288 bytesDatabase Buffers 2432696320 bytesRedo Buffers 15593472 bytesDatabase mounted.Database opened.SQL>