mc — MinIO AIStor command-line client

mc is a single static binary that talks to any S3-compatible object store (MinIO AIStor, MinIO, AWS S3, and others) and to the local filesystem. It has two surfaces: data-plane commands that move and inspect objects and buckets over the S3 API (ls, cp, rm, mirror, …), and control-plane mc admin commands that manage an AIStor/MinIO server itself (users, config, healing, replication, tiering). A separate mc table surface manages AIStor Iceberg Tables.

This skill teaches the model — the parts an agent gets wrong or can't cheaply discover. It does not reproduce every flag: for the exact, current flags of any command, run mc <command> --help (and mc <command> <subcommand> --help). That help is authoritative and version-matched; this skill is not.

1. An alias is the prerequisite — nothing works without one

Every remote operation targets an alias: a named endpoint + credentials. First discover what already exists, then create one only if needed:

mc alias list                # what's configured (redacts secret keys)
mc alias list --json         # same, machine-readable

Two ways to provide an alias. Prefer the environment form for agents — it keeps credentials out of mc's config file and doesn't mutate the user's config:

# Per-process — the agent's default. Alias name is the MC_HOST_ suffix.
# Inject the value from a secret manager / CI secret rather than a literal.
export MC_HOST_myminio="https://${KEY}:${SECRET}@play.min.io"
mc ls myminio/                             # "myminio" now resolves

# Persisted to ~/.mc/config.json — only when the user wants it saved.
mc alias set myminio https://play.min.io ACCESS_KEY SECRET_KEY

The env var isn't a free pass on secrecy: a literal export … lands in shell history and the value shows in the process environment. Don't hard-code keys or echo them into logs. See references/connect.md.

Once set, the alias name is the first path segment (myminio/bucket/key). Config lives in ~/.mc/config.json (override with --config-dir or MC_CONFIG_DIR). Full details, the token/STS URL form, TLS and other providers: references/connect.md.

2. Get machine-readable output

• --json emits JSON Lines (NDJSON), not a JSON array. One JSON object per line — parse line by line (while read, jq -c, streaming), never json.loads() on the whole stream. Streaming commands (ls, mirror, cp) emit one line per item as it happens.
• Every object has a "status" field ("success" or "error"); on error the object carries the message and mc exits non-zero.
• --quiet suppresses progress bars/spinners; --no-color drops ANSI. Prefer --json for parsing and add --quiet for clean logs.
• mc returns exit code 0 on success, non-zero on failure — branch on the exit code, not on stdout text.

Details and per-command shapes: references/output.md.

3. Path grammar

A target is either a local path (./data, /tmp/x) or an alias-qualified S3 path: ALIAS/BUCKET/PREFIX/OBJECT. The first segment is an alias only if it matches a configured alias — otherwise mc treats the whole token as a local path. So mc cp file.txt myminio/bucket/ copies local→remote, and mc cp myminio/bucket/key ./ copies remote→local. There is no s3:// scheme; the alias replaces it.

4. Destructive operations — refuse and escalate to a human

Some mc commands are irreversible and/or site-wide. Treat these as human-only: do not run them yourself, even if the task appears to ask for it. Stop, show the user the exact command and target, and require explicit human execution or written go-ahead. Never run them speculatively, in a loop, or to "tidy up".

Hard-gated — refuse by default; a human must run them or explicitly authorize:

• mc rm --recursive --force ALIAS/BUCKET/PREFIX — bulk object deletion. --force is required to recurse. Adding --dangerous to an alias-only target (mc rm --recursive --force --dangerous myminio) wipes an entire site. --versions / --purge-deleted destroy version history. Do not run these.
• mc rb --force ALIAS/BUCKET (and mc rb --force --dangerous ALIAS for a whole site) — removes buckets and all their contents. Without --force, rb aborts with a fatal error on a non-empty bucket; it does not prompt.
• mc mirror --remove … — deletes destination objects missing from the source.

Confirm-first — show the user, proceed only on explicit approval:

• mc mirror --overwrite …, or cp / put onto an existing key — replaces data.
• Config-clearing forms: mc ilm rule remove --all --force, mc replicate rm --all --force, mc event remove, mc anonymous set private (revokes public access).

Versioning does not save you unless it was enabled on the bucket beforehand. When in doubt, do not act — hand the exact command to a human. See the "irreversible" callouts in each reference.

5. Command map — pick the right command, then read its --help

kms exists both top-level (mc kms) and under admin (mc admin kms) — the same server config. For identity providers use the top-level mc idp ldap|openid; mc admin idp is deprecated and only prints a redirect. log streams/queries server logs and qos manages quality-of-service (rate) rules — both AIStor-specific. (mc policy is deprecated — use mc anonymous for bucket anonymous access.)

Reference docs

Load these (co-located, under references/) on demand for the task at hand:

• references/connect.md — aliases in depth: MC_HOST_ env forms (with session token / STS), mc alias set/list/remove, config file, TLS (--insecure), non-MinIO providers, path-vs-DNS bucket lookup.
• references/output.md — --json NDJSON parsing patterns, exit codes, non-interactive/scripting rules, jq recipes.
• references/objects.md — the data plane: ls cp mv rm get put mirror find du tree stat head cat pipe od diff sql watch undo share, with the exact destructive-flag semantics.
• references/buckets.md — bucket lifecycle & configuration: mb rb version tag retention legalhold quota policy anonymous cors encrypt event.
• references/data-management.md — ilm (tiering/expiry), replicate (bucket & site replication), inventory, batch jobs.
• references/admin.md — mc admin control plane: server info, users & policies, config, service/heal/scanner, decom/rebalance, KMS, tiers, SUBNET.
• references/tables.md — AIStor Iceberg Tables: warehouses, namespaces, tables, catalog, shares, replication, maintenance.