14.5 Disk Exhaustion
peipkg checks free space before it stages anything, so exhaustion normally arrives as a refusal that costs nothing. A write can still fail — another process can consume the space in between, and the estimate is of payload rather than of the metadata the filesystem writes alongside it — and where in the operation that happens decides how bad it is.
14.5.1 During staging #
The cleanest case. Nothing has been renamed into place, the transaction rolls back, and the staged files are discarded — recovering the space they consumed.
14.5.2 During the apply phase #
Some files have been renamed in and some originals are sitting at their backup paths.
Because backups are renames rather than copies, the apply phase itself consumes almost no additional space: the space was consumed during staging. A failure here is more likely to be a different error than exhaustion.
Rollback restores from the backup map, which is again renames, so it does not need space either.
14.5.3 During the commit #
The database commit needs space for its own write-ahead log. A failure there leaves the transaction uncommitted, and rollback proceeds normally — but a database that cannot write is a database that cannot record a rollback, which is where §14.2 begins.
14.5.4 The check #
A transaction's requirement is the incoming file content of its added and replaced entries, aggregated across every operation. Backups cost nothing, because they are renames rather than copies, and a removal frees rather than consumes. A replaced file's old bytes are not subtracted: they are still on disk under the backup name until the commit succeeds, which is exactly when the space is needed.
The figure is computed per filesystem, not as a single total, because a transaction can span several — installation roots and destinations within a root can be separate mounts. Destinations are grouped by the filesystem id their directory reports, so the mount table never has to be read.
The comparison is against the blocks available to an unprivileged writer, not the free blocks: the reserved fraction is not peipkg's to spend. A 32 MiB margin is left on top, covering the inodes, directory entries, journal blocks and tail padding the filesystem writes that the payload figure does not include. The check runs before the journal is opened, so a refusal leaves nothing to recover from.