Be careful to use the cryptographic one, not rand(3)
And if you're a sysadmin, be extremely careful when generating keys in VMs or embedded devices. They tend to overestimate their entropy sources - it's possible that every clone of a VM generates the same keys. In some cases (cough ECDSA) generating the same key and nonce to sign two different messages is catastrophic - it immediately leaks the private key.
good point about VMs. if you run some VPS your provider could just link in a shitty rng into the thing and not give access to the correct hardware rng. U'd really need to dig into that to find out :/.
And if you're a sysadmin, be extremely careful when generating keys in VMs or embedded devices. They tend to overestimate their entropy sources - it's possible that every clone of a VM generates the same keys. In some cases (cough ECDSA) generating the same key and nonce to sign two different messages is catastrophic - it immediately leaks the private key.