get error when occlum build --sgx-mode SIM

[yzhdut]

root@node:~/occlum_workspace/occlum_instance# occlum build --sgx-mode SIM
Enclave sign-tool: /opt/occlum/sgxsdk-tools/bin/x64/sgx_sign
Enclave sign-key: /opt/occlum/etc/template/Enclave.pem
SGX mode: SIM
Building new image...
[+] Home dir is /root
[-] Open token file /root/enclave.token error! Will create one.
/bin/bash: line 7: 8390 Killed LD_LIBRARY_PATH="/opt/occlum/sgxsdk-tools/sdk_libs" /opt/occlum/build/bin/sefs-cli_sim --enclave "/opt/occlum/build/lib/libsefs-cli.signed.so" zip $SECURE_IMAGE_KEY_OPTION "/root/occlum_workspace/occlum_instance/image" "/root/occlum_workspace/occlum_instance/build/mount/__ROOT" "/root/occlum_workspace/occlum_instance/build/mount/.ROOT_MAC"
/opt/occlum/build/bin/occlum_build.mk:132: recipe for target '/root/occlum_workspace/occlum_instance/build/mount/__ROOT/metadata' failed
make: *** [/root/occlum_workspace/occlum_instance/build/mount/__ROOT/metadata] Error 137

Can anybody help me?