IEC020I: 001 abend, I/O error with no error routine

What it means

Programs that read and write sequential files, libraries and direct files go through access methods such as QSAM, BSAM and BPAM. A program can give the access method an error routine, called a SYNAD exit, to deal with I/O errors. When an error happens and there is no SYNAD exit, or the exit returns and lets the error stand, the access method can't go on. z/OS writes IEC020I and ends the step with abend 001.

The message has two forms. For a data set on a device, it gives the abend and return code, the module, the job and step names, the DD name, the device number, the volume serial and the data set name. For a SYSIN or SYSOUT data set or a z/OS UNIX file, the last field is a code instead. USS means a UNIX file, JES means a subsystem data set, and three or four hex digits are a device number.

The return codes are single digits. 0 means the record length or block size in the program or the DD statement doesn't match the data set. 1 means an I/O error with no SYNAD exit. That includes a real device error, but also writing to a file opened for input, reading one opened for output, RECFM=U with no record length, and a concatenated data set whose attributes differ from the first one in a way the open couldn't catch. 2 means an error while closing the data set. 3 and 4 are QSAM cases where the error options in the DCB didn't allow the program to carry on. 5 means a QSAM GET after end of file. 6 means a positioning error while reading a UNIX file.

For a partitioned concatenation, the data set name in the message is the first one in the concatenation, which may not be the one that failed.

Common causes

• The record length or block size coded in the program or on the DD statement doesn't match the data set (return code 0).
• The program asked QSAM for another record after it had already reached end of file (return code 5). This is a logic error in the program's read loop.
• A data set in a concatenation has a different record format, length or block size from the first one.
• The program wrote to a file it opened for input, or read one it opened for output.
• A real hardware or media error on the disk or tape. In that case IEA000I appears in the job log as well.
• An error while the data set was being closed (return code 2).

How to find the problem

1. In SDSF, open JESYSMSG and find IEC020I. Note the return code after 001, the DD name and the data set name.
2. Look for IEA000I just before it. If it is there, the cause is a device or media error rather than the program.
3. For return code 0 or 1, compare the data set's real attributes (ISPF option 3.4, I line command) with the DCB values on the DD statement and the record layout in the program.
4. If the DD name has a hyphen and a number after it, or names a concatenation, check every data set in that concatenation. The one the message names may not be the one at fault.
5. For return code 5, look at the program's read loop and how it handles end of file.

How to fix it

• Remove hard-coded LRECL or BLKSIZE values from the DD statement for existing data sets, and make the program's record length match the data set.
• Fix the read loop so it stops after end of file.
• Make every data set in a concatenation use the same record format and record length, or split them into separate steps.
• Open the file in the mode the program really uses it.
• For a hardware or media error, pass IEA000I to the storage or operations team. Restore the data set from a backup if it is damaged.

Last reviewed 2026-10-18 by the WND Software team. Written in our own words. For the full reference, check IBM’s documentation for your z/OS release.