1. Question

When installing the virtual machine, the system does not set the swap size or the memory is too small. The compiler will have the problem of virtual memory exhausted: cannot allocate memory. You can use swap to expand memory.

2. Solution

When free – M is executed, the prompt cannot allocate memory:

(swap files can be placed in their favorite location, such as/var/swap)

[root@Byrd byrd]# free -m
             total       used       free     shared    buffers     cached
Mem:           512        108        403          0          0         28
-/+ buffers/cache:         79        432
Swap:            0          0          0
[root@Byrd ~]# mkdir /opt/images/
[root@Byrd ~]# rm -rf /opt/images/swap
[root@Byrd ~]# dd if=/dev/zero of=/opt/images/swap bs=1024 count=2048000
2048000+0 records in
2048000+0 records out
2097152000 bytes (2.1 GB) copied, 82.7509 s, 25.3 MB/s
[root@Byrd ~]# mkswap /opt/images/swap
mkswap: /opt/images/swap: warning: don't erase bootbits sectors
        on whole disk. Use -f to force.
Setting up swapspace version 1, size = 2047996 KiB
no label, UUID=59daeabb-d0c5-46b6-bf52-465e6b05eb0b
[root@hz mnt]# swapon /opt/images/swap
[root@hz mnt]# free -m
             total       used       free     shared    buffers     cached
Mem:           488        481          7          0          6        417
-/+ buffers/cache:         57        431
Swap:          999          0        999

Memory is too small. Increasing memory can solve this problem

You can turn off swap after use:

[root@hz mnt]# swapoff swap
[root@hz mnt]# rm -f /opt/images/swap

Swap files can also not be deleted and kept for future use. The key is that your virtual machine hard disk is enough.