WARN Exec socket appeared but heartbeat failed, exec will not be available

[colorfulshark]

Hi guys,

I would like to use this project as a light weight sandbox, but had some trouble running the example.

I installed the binaries with

cp a3s* lib /usr/local/bin
ln -s /usr/local/bin/lib/libkrunfw.so* /usr/local/lib/

And when I try to launch the very start box, It outputted some error log

root@ai45lab:~# a3s-box run --name hello alpine:latest -- echo "Hello from MicroVM"
Creating box hello (a143eb40fcda)...
2026-04-21T07:34:20.157417Z  WARN Exec socket appeared but heartbeat failed, exec will not be available
Box hello (a143eb40fcda) started. Press Ctrl-C to stop.
init.krun: entered main argc=1
init.krun: mount_filesystems ok
init.krun: after cmdline env import KRUN_INIT=/sbin/init KRUN_INIT_PID1=<null> BOX_EXEC_EXEC=echo
init.krun: root propagation ok
init.krun: tty/session configured
init.krun: config parsed
init.krun: selected exec=/sbin/init init_pid1=0
init.krun: setup_redirects ok
init.krun: execvp(/sbin/init) starting
init.krun: execvp(/sbin/init) failed errno=2
Couldn't execute '/sbin/init' inside the vm: No such file or directory

Stopping box hello...
Box hello stopped.

I also tried running a box with interactive shell, still got errors

root@ai45lab:~# a3s-box run -it --name dev alpine:latest -- /bin/sh
Creating box dev (3a4989f02274)...
2026-04-21T07:47:58.636724Z  WARN Exec socket appeared but heartbeat failed, exec will not be available
Error: Exec error: Failed to connect to PTY server at /root/.a3s/boxes/3a4989f0-2274-4ef8-bef1-26a645a81af2/sockets/pty.sock: Connection refused (os error 111)

Appreciate for your help.

[ZhiXiao-Lin]

Hi, thanks for reporting this issue. To help diagnose the root cause, could you please provide the following information:

System Information

1. Machine type — What CPU architecture? (e.g., x86_64, aarch64)
2. Host OS — What Linux distribution and version are you running on? (e.g., Ubuntu 22.04, Debian 12)
3. a3s-box version — What version of a3s-box are you using?

   a3s-box --version

Installation Details

4. How did you install a3s-box? (from source, binary release, homebrew, etc.)

5. **What's the full contents of your /usr/local/bin and /usr/local/lib directories?

   ls -la /usr/local/bin/a3s* /usr/local/lib/libkrun* 2>/dev/null

6. **Is the guest init binary present?

   find /usr/local/bin -name \"*guest-init*\" 2>/dev/null
   # Also check in lib dir
   find /usr/local/lib -name \"*guest-init*\" 2>/dev/null

Debugging

7. Can you run with verbose debug logging? Try:

   RUST_LOG=debug a3s-box run --name hello alpine:latest -- echo \"Hello\"

8. Check if the rootfs was built correctly — look for the box directory that was created:

   ls -la ~/.a3s/boxes/*/rootfs/sbin/init 2>/dev/null
   file ~/.a3s/boxes/*/rootfs/sbin/init 2>/dev/null

9. What does `strace` show? If available:

   strace -f a3s-box run --name hello alpine:latest -- echo \"Hello\" 2>&1 | grep -E \"(execve|sbin/init|BOX_EXEC)\" | head -30

This will help determine whether:

• The guest init binary is missing from your installation
• The guest init is not being installed into the rootfs
• The `BOX_EXEC_EXEC` environment variable is not being passed correctly to the VM

[colorfulshark]

Hi, thanks for reporting this issue. To help diagnose the root cause, could you please provide the following information:

System Information

1. Machine type — What CPU architecture? (e.g., x86_64, aarch64)
2. Host OS — What Linux distribution and version are you running on? (e.g., Ubuntu 22.04, Debian 12)
3. a3s-box version — What version of a3s-box are you using?
   a3s-box --version

CPU: AMD Ryzen H255
Host OS: Debian 13
a3s-box version: 2.0.0

Installation Details

4. How did you install a3s-box? (from source, binary release, homebrew, etc.)
   Download binary from github release and install manually.
5. What's the full contents of your /usr/local/bin and /usr/local/lib directories?
   ls -la /usr/local/bin/a3s /usr/local/lib/libkrun 2>/dev/null

root@ai45lab:~#  ls -la /usr/local/bin/a3s* /usr/local/lib/libkrun* 2>/dev/null
-rwxr-xr-x 1 root root 23345633 Apr 21 07:32 /usr/local/bin/a3s-box
-rwxr-xr-x 1 root root 15669697 Apr 21 07:32 /usr/local/bin/a3s-box-cri
-rwxr-xr-x 1 root root  5165632 Apr 21 07:32 /usr/local/bin/a3s-box-guest-init
-rwxr-xr-x 1 root root  4457417 Apr 21 07:32 /usr/local/bin/a3s-box-shim
-rwxr-xr-x 1 root root  5538225 Apr 21 06:35 /usr/local/lib/libkrun.so
-rwxr-xr-x 1 root root  5538225 Apr 21 06:35 /usr/local/lib/libkrun.so.1
-rwxr-xr-x 1 root root  5538225 Apr 21 06:35 /usr/local/lib/libkrun.so.1.17.0
lrwxrwxrwx 1 root root       31 Apr 21 07:33 /usr/local/lib/libkrunfw.so -> /usr/local/bin/lib/libkrunfw.so
lrwxrwxrwx 1 root root       33 Apr 21 07:33 /usr/local/lib/libkrunfw.so.5 -> /usr/local/bin/lib/libkrunfw.so.5

6. **Is the guest init binary present?
   find /usr/local/bin -name "guest-init" 2>/dev/null

root@ai45lab:~# find /usr/local/bin -name "*guest-init*" 2>/dev/null
/usr/local/bin/a3s-box-guest-init

Also check in lib dir

find /usr/local/lib -name "guest-init" 2>/dev/null

root@ai45lab:~# find /usr/local/bin -name "*guest-init*" 2>/dev/null
/usr/local/bin/a3s-box-guest-init

root@ai45lab:~# find /usr/local/lib -name "guest-init" 2>/dev/null
root@ai45lab:~# 

Debugging

7. Can you run with verbose debug logging? Try:
   RUST_LOG=debug a3s-box run --name hello alpine:latest -- echo "Hello"

Too many logs but end with
[2026-04-21T09:28:55Z DEBUG vmm] using vmm exit code: 127
[2026-04-21T09:28:55Z INFO  vmm] Vmm is stopping.
2026-04-21T09:28:56.105809Z DEBUG vm_boot{box_id=781ec7fe-754c-46eb-ace0-6cb62781777f}:wait_for_ready: VM process is running
2026-04-21T09:28:56.105851Z DEBUG vm_boot{box_id=781ec7fe-754c-46eb-ace0-6cb62781777f}:wait_for_ready: Waiting for exec server socket socket_path=/root/.a3s/boxes/781ec7fe-754c-46eb-ace0-6cb62781777f/sockets/exec.sock
2026-04-21T09:28:56.105887Z DEBUG vm_boot{box_id=781ec7fe-754c-46eb-ace0-6cb62781777f}:wait_for_ready: Exec socket file detected
2026-04-21T09:28:56.105963Z DEBUG vm_boot{box_id=781ec7fe-754c-46eb-ace0-6cb62781777f}:wait_for_ready: Exec connect failed, retrying error=Exec error: Failed to connect to exec server at /root/.a3s/boxes/781ec7fe-754c-46eb-ace0-6cb62781777f/sockets/exec.sock: Connection refused (os error 111)

8. Check if the rootfs was built correctly — look for the box directory that was created:
   ls -la ~/.a3s/boxes/*/rootfs/sbin/init 2>/dev/null

root@ai45lab:~# ls -la ~/.a3s/boxes/*/rootfs/sbin/init 2>/dev/null
-rwxr-xr-x 1 root root 5338136 Apr 21 06:26 /root/.a3s/boxes/02245875-3cfe-481e-930c-d9c6b7a8ac61/rootfs/sbin/init
-rwxr-xr-x 1 root root 5338136 Apr 21 06:35 /root/.a3s/boxes/157b339a-fac1-42b7-b136-445e1ac08ea2/rootfs/sbin/init
-rwxr-xr-x 1 root root 5338136 Apr 21 07:47 /root/.a3s/boxes/3a4989f0-2274-4ef8-bef1-26a645a81af2/rootfs/sbin/init
-rwxr-xr-x 1 root root 5165632 Apr 21 06:30 /root/.a3s/boxes/50d12f99-f2d1-4b83-99ee-965d63614c55/rootfs/sbin/init
-rwxr-xr-x 1 root root 5338136 Apr 21 09:28 /root/.a3s/boxes/77f493d4-9c1a-4526-9b31-67232e6185a7/rootfs/sbin/init
-rwxr-xr-x 1 root root 5338136 Apr 21 09:28 /root/.a3s/boxes/781ec7fe-754c-46eb-ace0-6cb62781777f/rootfs/sbin/init
-rwxr-xr-x 1 root root 5338136 Apr 21 06:29 /root/.a3s/boxes/a5c81bda-b5fa-4981-a588-12d412a42f49/rootfs/sbin/init
-rwxr-xr-x 1 root root 5338136 Apr 21 09:17 /root/.a3s/boxes/c20851dd-8164-41c4-af7f-232f9b591ad3/rootfs/sbin/init
-rwxr-xr-x 1 root root 5338136 Apr 21 09:17 /root/.a3s/boxes/e9637925-cbc4-40ff-91d6-bb0b163686bc/rootfs/sbin/init
-rwxr-xr-x 1 root root 5338136 Apr 21 09:28 /root/.a3s/boxes/f99ea77d-3ee5-4836-90ac-31be5980a983/rootfs/sbin/init

file ~/.a3s/boxes/*/rootfs/sbin/init 2>/dev/null

/root/.a3s/boxes/02245875-3cfe-481e-930c-d9c6b7a8ac61/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped
/root/.a3s/boxes/157b339a-fac1-42b7-b136-445e1ac08ea2/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped
/root/.a3s/boxes/3a4989f0-2274-4ef8-bef1-26a645a81af2/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped
/root/.a3s/boxes/50d12f99-f2d1-4b83-99ee-965d63614c55/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), static-pie linked, BuildID[sha1]=fbc9fdc0af3584321e0f60e54899e6255e2d59db, not stripped
/root/.a3s/boxes/77f493d4-9c1a-4526-9b31-67232e6185a7/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped
/root/.a3s/boxes/781ec7fe-754c-46eb-ace0-6cb62781777f/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped
/root/.a3s/boxes/a5c81bda-b5fa-4981-a588-12d412a42f49/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped
/root/.a3s/boxes/c20851dd-8164-41c4-af7f-232f9b591ad3/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped
/root/.a3s/boxes/e9637925-cbc4-40ff-91d6-bb0b163686bc/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped
/root/.a3s/boxes/f99ea77d-3ee5-4836-90ac-31be5980a983/rootfs/sbin/init: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=843eb736ca1b3963d8fc1c112e144341b6860d96, not stripped

9. What does strace show? If available:
   strace -f a3s-box run --name hello alpine:latest -- echo "Hello" 2>&1 | grep -E "(execve|sbin/init|BOX_EXEC)" | head -30

no output

This will help determine whether:

• The guest init binary is missing from your installation
• The guest init is not being installed into the rootfs
• The BOX_EXEC_EXEC environment variable is not being passed correctly to the VM