EC
EHOSTDOWN
Linux / POSIXERRORNotableNetworkHIGH confidence

Host Is Down

Production Risk

Indicates server or host outage; implement retry with exponential backoff.

What this means

EHOSTDOWN (errno 112) is returned when a connect() or send() fails because the remote host is down. This is typically returned by NFS or when an ICMP "Host is down" message is received.

Why it happens
  1. 1NFS server is powered off or crashed
  2. 2ICMP destination unreachable (Host is down) received
  3. 3Remote host not responding to ARP on the local network
How to reproduce

NFS operation when the file server is down.

trigger — this will error
trigger — this will error
// NFS read when server is down
ssize_t n = read(nfs_fd, buf, sizeof(buf));
// Returns -1, errno = EHOSTDOWN

expected output

read: Host is down (EHOSTDOWN)

Fix

Verify host is reachable before operating

WHEN After EHOSTDOWN

Verify host is reachable before operating
# Check if host is up
ping -c 3 nfs-server
# Check NFS service
showmount -e nfs-server
# Remount after server recovery
mount -a

Why this works

EHOSTDOWN is terminal for the operation; wait for the host to recover and reconnect.

Sources
Official documentation ↗

Linux Programmer Manual errno(3)

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